Heating mat vs Flexwatt heat tape

My current set-up has 2 identical heating mats connected to a thermostat (Helix); spread across 4 glass tanks (1 heat mat per 2 tanks). The problem is, I'm getting different temperatures from the 2 mats. The thermostat is set to 92F, one heating mat is constant at 90-91F, but the other one (closer to window) could only get to 85-86F. It could be that particular heating mat not working well, I'll change for another one tonight to see if that'll fix it. If not, I'm seriously considering switching to Flexwatt heat tape instead. So I'll only have one heating element connected to a thermostat.

Since heat tape are a lot cheaper than heating mats, what are the pros and cons that I need to consider?

p.s. My females set up is the same, 3 smaller heating mats connected to 1 Helix unit; 2 tanks have the right temp, but the last one is 3-4 degrees lower and its the furthest away from the window.

I use uth's right now and for christmas Im getting flexwatt tape and a thermostat, I don't know the pros and cons but I think a pro is temps will be more stable.

I found this website for flexwatt 3 inch for like 2.20 US, thats the cheapest ive seen it, http://www.mgreptiles.com/flexwatt.html

If I'm switching to flexwatt, I think I'll go for the 11 inch ones. My tank dimension is 16" wide x 21" length. Will heat tape provide steady temp throughout the whole length; or will there still be discrepancy from one end to the other?

I don't know how it will be under different tanks, but my opinions is that it should stay the same temp. I use flexwatt and I have no discrepancies, but I use a different piece under each tank and they are all plugged into one thermostat.