3) Consumer Considerations

Certain things must be considered when choosing which product is best for your needs.
The three main catagories examined here are:
Effectiveness/Durability
Application
Cost

Effectiveness and Durability

       As discussed earlier in the Science section, previous studies have found that at peak performance PDMS based repellents allow water to slide off at a smaller angle. This means that Rain-x which uses PDMS has a stronger repelling effect on water than Aquapel at peak performance [1]. For uses that require the highest possible performance, Rain-X may be the best option because Aquapel is not as effective. Although Rain-X has a higher peak performance, this comes at a cost. Rain-X also has a short life span and durability. Some users have reported problems in as little as 20 days after application. On the other hand  Aquapel is strongly chemically bonded to the glass it can go even as long as 6 months without severe degradation. Some users report times as long as 8 months without reapplication [2]. The following video compares  Aquapel to Rain-X over time:

Application

To apply Rain-x the user first applies rain-x using small circular motions over the entire windshield. After applying the product must sit for a few minutes to haze over. After this haze appears, it must be buffed out completely using a new dry cloth This buffing stage can be difficult and tedious to complete due to the fact the haze is often hard to buff out. Rain-x also recommends multiple applications for full effect. Even with extensive buffing, some users still angrily report streaks and hazing.

To apply Aquapel the user moves the applicator all over the windshield in both horizontal and vertical motions. This can take significantly less time due to the fact that there is no requirement for small circles. After the initial application stage, the user wipes off the excess with a paper towel. No buffing is required if wiped up immediately. This can save a significant amount of time as rain-x requires a large amount of buffing, following the already lengthy application.  Aquapel also does not require more than one application, which means rain-x application can take over twice the time for a similar effect

Also due to the problems with durability discussed earlier, Rain-x needs to be applied every couple weeks, sometimes as often as every 20 days to retain effect. This can add more time to an already lengthy application. Aquapel on the other the other only needs to be applied every 6 months at the very most.

Cost

The cost for a spray bottle of rain-x Glass cleaner and rain repellent is $9.42 for a 23oz bottle on Amazon [3]. There are cheaper alternatives but these do not include the glass cleaner which is necessary. After factoring that in it comes out to about $10. This bottle is good for a number of uses as it appears the application takes an ounce or less.

Aquapel on the other hand is $11.95 for four single use applicators [4]. Though this is more expensive per application, looking back on the durability, Aquapel lasts significantly longer. In the worst case, Aquapel is a little bit more expensive for a longer lasting repellent. In the best case, its durability allows it to be a cost effective alternative to rain-x. Cost/benefit depends on a number of factors including how effectively and how often either repellent is applied.

One hidden cost that user may not see comes from windshield repair. Because Rain-X is not completely bonded to the windshield, it has the ability to be moved around as discussed earlier. If a crack or chip happens to appear in the windshield, Rain-X can seep into the crack. Due to its hydrophobic nature, Rain-X can actively prevent correct repair of cracks, which may necessitate the complete replacement of a slightly damanged windshield [5]. Aquapel on the other hand does not slowly move around windshields and cannot fill into cracks unless the chemical was applied directly to a crack [6]. In the long term, Aquapel may save tremendous money on windshield replacement.




Conclusion:

Based on all the evidence provided Aquapel seems to be the clear leader in terms of the best water repellent on the market for use by consumers. Aquapel although slightly less effective, has a significantly longer durability. It can last up to 8 times longer than Rain-X. Application is easier quicker and less of a hassle than Rain-X especially due to the fact that no hazing will occur with Aquapel. Lastly, although the cost over time may be hard to estimate, there are significant benifits for windshield repair while using Aquapel over Rain-X.
In conclusion: Aquapel is better choice to use a rain repellent in almost all conditions.
As with any technology, hydrophobic water repellents are constantly going through innovation. In 2003 the Nippon Glass Laboratory [1] was successful in designing a new type of FAS which actually has a comparable effectiveness to PDMS but still retains the advantage of increased durability. Although this new FAS probably has not made it to market yet, these new types of innovations are happening regularly and can easily create a huge impact on the market. Currently though there is a clear leader, Aquapel, in the water repellent debate.

References
[1] Development of Water-Repellent Glass Improved Water-Sliding Property and Durability http://www.springerlink.com/content/x72674302445h130/fulltext.pdf

[2] Rain-X vs Aquapel http://www.jwardell.com/mini/2006/10/20/reviews-in-review/

[3] Rain-X cost on Amazon http://www.amazon.com/Rain-X-5071268-2-In-1-Cleaner-Repellent/dp/B000NWJJLG/ref=sr_1_5?ie=UTF8&qid=1330677276&sr=8-5

[4] Aquapel cost on Amazon http://www.amazon.com/Aquapel-Glass-Treatment-Single-Applicators/dp/B004NFU300/ref=sr_1_1?ie=UTF8&qid=1330680570&sr=8-1

[5]  More Rain-x Havoc Coming for Windshield Repair, via Car Washes and Windshield Washer Fluids.

http://www.windshieldrepairtools.com/More%20Rain%20Havoc.htm

[6] Aquapel Frequently Asked Questions http://www.aquapel.com/FAQ.php