I use an EGO mostly, better battery life, etc, etc... but if you want something small, it is a trade off between form and performance. Just the way it is......
I have a 4081 (Safe Cig) also. i still puff on it sometimes as i like the taste it provides. I just ordered a SmokeStik battery also as i want to compare the difference and one of my Safe Cig batteries went poof already - after a month. That is another issue with the small ecigs - it is a lot of strain for a small battery...
As far as KR808 a lot of people like them. i don't care for mine. You will find that all models have a different flavor/taste. This has to do with the type of cartomizer - not the battery type.
I likely will get a 4081 adapter for my EGO. Then I will have battery life when i want - or small when i want - and still use the same cartomizers. Many prefer the atty/cart combo. That is another thing to consider - the one you have is 2 piece - Battery + cartomizer. Most are 3 piece - battery +atomizer + cartridge. However, a 3 piece model can use a cartomizer instead, essentially making them a 2 piece model, if you prefer that setup.
Bottom line: If you are ok with bigger, then EGO or RIVA (EGO knockoff - cheaper). If you have to get something else small - makes the choice quite a bit more difficult. GreenSmoke is an E9, not a great model. But all minis are going to have battery life issues - just the way it is.
Either way, if you order anything, make sure you get the discount codes for ECF members!