I love mine; have now had them in use for 8-9 years. I do the same as mentioned by another poster; take an empty bucket around w/ me when it's time to clean them out and refill. I let the water level get fairly low, then take empty bucket,and long-handled scrub brush around, scrub, dump, refill w/ clean water--not hard! I stick my fingers in the water fairly often to check that there isn't any 'shocking' happening!
I use the little 2 1/2 gal. buckets inside the barn, 5 gal. ones outside. I plug two into a multi-head HD outdoor ext. cord (protecting the plug from moisture), and that is plugged into a HD grounded timer. I set the timer to match the on and off-peak hours from my electric coop; works most of the time, though if it gets REALLY cold, I set the timer so that the heaters are 'on' for more hours. This was a tip from the electrician who installed the electric out to my mare pen(two spotlights and a box w/the light switches and two outdoor plugs; I use a floating tank heater there, in my 72 gal. stock tank, but a similar 'set-up')-sure helps w/ the overall electric bill. That said--the 5 gal. heated buckets pull only 36 watts; the smaller ones, even less; the floating tank heater, 1000 watts (most catalogs only offer the 1500 watt one, but I make sure to get the 1000 watt, because I simply don't NEED the higher wattage, and it saves considerably on electricity! Mine are API, the red ones; I use a galvanized tank.
I had one 16 gal. size(the 'muck bucket' size, and it does have a replaceable heating element), but it was for my 'big' Paint mare, so haven't used it since winter before last. The 5 gal. are plenty big for one mini. The 16 gal.pulls about twice(?) as much wattage as the 5 gal., but still, worth it to not have to deal w/ frozen drinking water, or a colic from not enought water intake!
IMO-mostly pros, few cons. Keep everything in good repair and check frequently to see that it is staying that way.
Margo