here is the flexwatt Q&A page on matts site : http://www.mgreptiles.com/FLEXFAQ.html

he is having a great sale right now, so it would be a great time to pick up a t-stat.

I have a 4 tub rack that used 1' strips of 11'' flexwatt. That heats tubs that are 31x17x6. I would definately recommend getting a t-stat if you can. But a dimmer(matt sells them too) will work if you cant afford one. Hope that helps a bit.