Yes flexwatt can be controlled by a herpstat just remember out of control flexwatt is very hot and potentially dangerous, there are UTH on the market (ultratherm and zoomed new ones I believe Kane as well) that are safer as they are restricted to a max temp. ( it is the max operation temp of flexwatt... hmmm what are the chances of that? )

There are basically two types of thermometer good and cheap. Good ones are out of the budget of most (100$-2000$ depending) the rest are all the same for the most part. Look at the specs the majority of thermometers are +/- 2ºF up or down. Some are +/-2ºC (some accurites are...) if you don't know metric that is just shy of 4ºF this means the tolerance in manufacture cannot guarantee results closer to correct that this. Some could be bang on some off by the max tolerance and still be ok according to the manufacturer.

The best way to get close to accurate is either test against something accurate (like a herpstat which is spec'd at +/- 0.9ºF ) or buy a few and test them against each other variations in unit to unit then become apparent and the ones that read together are usually very close to correct. I usually say 5+ but 3 will do in some cases. There is the issue with accurites too expensive to buy enough to find a good set. I also don't like seeing batteries in high humid enclosed conditions they can be prone to leaking battery acid and fumes. The units I buy are the cheapest I can find. I usually pay between 1$ to 4$ with shipping included. They are crap units but at an average of 2$ each I buy 20 of them. I usually get rid of 4 or so as being too far of correct and when the probe gets damaged they can be replaced. replacing accurites when the probe gets peed on or pinched get expensive quickly. I rarely keep thermometers longer than 18 months before they become damaged and incorrect. Sometimes all it takes is a door closing on the probe to throw it off a degree or so.

Hygrometers are a messy thing digital units are very fragile, dirt and junk alter the reading very quickly. They never seem to be accurate for long and some start with such a wide range of RH that it is useless anyway. (some digital units are 20% +/- so correct could be 60% but the hygrometer could read between 40-80% and still be 'accurate' according to the manufacturer. usually 5-10%RH is common.)

I recommend cigar analogue units. The things to look for are a METAL face card. Paper cards warp in humidity and this stops the movement (like pet store ones) the second thing is a calibration screw on the back. The test for analogue units is easy and cheap (salt test) it is accurate to 1% so there is no reason not to expect the analogue ones to be at farther off than 1% +/-. they are very tough too dust and dirt don't seem to effect them at all and I have one unit that ended up in a water bowl over a weekend and even a year later it is still correct.

personally I like the western instruments units but I suspect they are all from the same manufacturer. AVOID HAIR units they actually have a bit of hair that is used they are usually quite accurate but very fragile.

With out looking hard...
http://www.ebay.ca/itm/LCD-Digital-F...ht_3597wt_1165

This unit is interesting much more accuracy (0.5ºF) than the norm but it has wacky power supply issues.
http://www.ebay.ca/itm/280999317079?...ht_3625wt_1165

hygrometer
http://www.amazon.com/Analog-Hygrome...rds=hygrometer