The BAH is cheaper becasue it's a less high-tech, even lower-quality thermostat. With thermostats, the saying "you get what you pay for" definitely applies! The cheaper thermostats tend to be much more basic units... i.e., the 500R, the cheapest t-stat on the market (that I know of), is so basic it doesn't even have temperatures on a dial, has to be played with and adjusted to keep temps right, and has a reputation of failing in the first couple years of use.
Then you have the more expensive thermostats, i.e. Herpstat. This one is a digital, set-it-and-forget-it thermostat. Gives you temp readings within .1 degree (or, at least, the Herpstat II does--haven't used the I), and is VERY good at controlling temps, usually within 1 degree of the set temperature. The high/low alarms on the higher end Herpstats that Nanci mentioned are extremely helpful, too. There's been more than one occasion that the high/low alarm has saved my and my snakes' butts--especially since my big corn girl loves to knock her t-stat probe off the mat if it isn't anchored down. I can't count how many times, before I finally glued the thing down, the alarm woke me up in the middle of the night, just to find big girl dragged it off the heat mat while cruising for food--and under the bedding, of course, so I wouldn't be able to notice without digging around in the aspen.
If you have the money, spring for the Herpstat. Heck, spring for the Herpstat II or Pro... Definitely worth it, especially if you plan on expanding!
I am DEEPLY in love with my Herpstat II, and am in the same mindset as LostInstall. I wish I'd sprung for the Herpstat Pro when I got my II! (Especially since my parents paid for it... Lol!

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