I have both the 510 and 801 from eastmall. The 510's are just over a month old now and they work fairly well. Only problem I have with them is the cart performance, could never get one to last me more than about 3-4 drops worth (dry near the top, still soaked on the bottom), so I have to take a bottle of liquid everywhere. Tried most of the mods out there, slight improvements here and there, but still require an awful lot of attention to get it to perform at its best. When when it is performing, it's great.
Recently bought the manual 801 hoping to get more duration from the bigger carts. It has been 4 days and I'm very happy with it. Took around 40 drops of liquid fill a new cart and lasts me all day at work.
Obviously I can't speak much for reliability as everything is still new, but I've had no problem with the manual battery, everything is sealed, lasts quite a bit longer than 510 battery, it performs very consistantly until it starts flashing green (drained) and I think the switch have a better, quality feeling compared with the 510, it doesn't stick out as much (personal preference). Hopefully performance doesn't degrade tooo much as the 801 gets older. I will have to wait and see.
This week, I've been taking 801 to work and drip with 510 at home using a passthrough. Works pretty well.