A UTH should be around 1/3 the surface so a 9.8x5.9 might be big, about 1/2 I would look at smaller. The 20gal should be fine with a 13.8x8 unit. 10 and 20w seem high to me the ultratherms I have are larger 11x11 and only 15w. What ever unit is that size I might look to a lower wattage one unless it is internally regulated.
THe herpstats start at 100$ twice what you are look at.
Hydrofarms are hugely inaccurate the manufacturer lists the specs at (after you pester them forever) +/-4ºF with 3º additionally of hysteresis (how far over and under the set point it runs) this makes a 7º over the correct or 7º under correct possibility IF it is 100% correct according to the manufacturer. Personally many accept this kind of range (14ºF) I do not. Setting a thermostat at 90º I can live with 98-91ºF But have a hard time swallowing 83-97ºF. The only way I'd recommend a hydrofarm is if it is used with a accurate thermometer one that is certified and has specs of +/-1ºF or better. The stupid part of this is a thermometer that meets this is more expensive than a herpstat. This is my personal feeling on them. It is the one thing that insures health of a reptile over all others correct temps.
The big apple unit sounds better to me but again NO specs. What are they? You will have to ask Big Apple for the accuracy +/- ??? and what the hysteresis is. If you get anything worse than 2ºF with a 1ºF hysteresis I would avoid it. This is the specs for the Ranco and Johnson.
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