Well, here's my honest thoughts on my 901 (turns out to be RN4075, 901's cousin), as well as BE112 (801)... I don't have them anymore, as I sold them when I got my SD. They both have goods and bads.
901 tops the list for the taste and the size. Out of all my e-cigs, 901(4075) attys have given me the most consistent flavors. Decent throat hit w/o manual switch - but only when the battery is relatively full. Battery life was an issue for me, and that's why I jumped over to an SD.
801, originally intended to be my back-up unit. Excellent cartridge capacity - but the current design of 801 carts w/o any modification, at least for me didn't let me use all the juice in the cart. Most of the time, I was getting dry harsh hits from it. Even though BE112's atty is supposedly the most superior one out of all 801s, but it still had issue of not using the juice in entire capacity... only using upper half, and rest just stayed on the bottom... and in my retrospect, I should have re-stuffed the cartridge itself. I was consistently topping it off, which pretty much defeated its purpose of bigger cartridge. Decent battery life, and atomizer gives rather cold vapor. 901 is still pretty cool, compared to my other e-cigs like RN4081 (Npro) - but I kinda like warm vapor. Also, no matter how I look at it, it's pretty darn long and big. I had one atty that was really too tight for my carts, so I saw it off and made it much easier to "drip".. and it worked pretty well... but I believe cutting it off is more of an hastle than necessity too. Definitely better performing battery though - and I was even thinking making a custom 801 batt + 901 atty.
Truth is, no matter what I was using, I was topping off carts pretty often - much more so than I really wanted due to the filler issue. For me, it seems like it lost its full capacity in 1 or 2 full days of use.
If I'm to choose either one of them, I'll go with 901. It's just more of my likings in all around - perhaps except the shoddy 4075 cartridge.
