Automatic Fish Feeders - Opinions/Suggestions Wanted!

[PuffLuv]

In the past I have been fortunate enough to have someone come over to feed my livestock, however, that may change over Christmas. I would like to know everyone's opinion, and why they prefer one auto-feeder over another. The one I purchase will be used to feed a small amount of pellet food, 2-3 times daily. I have an open top, and a center brace that it could rest on or zip tie. However, a clamp-on might give more placement options and be more aesthetically pleasing. Also, some form of power backup is desirable (ie. batteries), however I could plug it into a UPS (Uninterruptible Power Supply)
Are some feeders more prone to clumping from moisture? (I do have an open top)

Auto Feeders I'm considering are:
http://www.jlaquatics.com/product/FD...od+Feeder.html

http://oceanaquatics.com/store/produ...r-Auto-Feeder/

http://www.jlaquatics.com/product/em...ic+Feeder.html

http://www.jlaquatics.com/product/fd...sh+Feeder.html

Is the heating module in the Rena much better than the air line with the Hydor? Also, light sensor....?

Are all of the feeders except the cheap one, a zip-tie installation?

Thanks for your input!