I have the al85 (as well as the alien, h-priv and g320).
I've found all the smok mods to work excellently.
As usual it's very important to make sure you have legit high quality batteries and if you will be ramping up the wattage make sure your battery can handle the correct discharge rate. I use a Samsung 25r in mine and it works perfectly. Sometimes I charge it via USB sometimes I charge it by taking the battery out. Both ways have continued to work fine with no problems.
I would recommend you don't vape on it whilst it's charging though as I did this on my g320 and it killed my usb supply (the draw must have carried straight past the battery to the usb port).
When it comes to buying batteries don't use eBay. That's a given with anything you need to be of guaranteed quality. It's flooded with fakes. Why take a risk of a nasty lithium vent (like a firework going off) potentially in your hand, face, pocket or house when you can buy cheaply from somewhere like fogstar (if you're in the UK that is). Use a reputable vendor for batteries every time.
Personally I think the best batteries are the Sony vtc5a they have a very good capacity plus the ability to discharge at higher amps than pretty much all others of similar capacities.
Look up moochs battery chart. It's essential for vapers using 18650 batteries.
I've got 2 tfv8 baby beast tanks and have tried all coils and not had one that tasted bad yet ( the rba is great as well), they have around a quarter of a tank break in to get rid of initial cotton taste but apart from that it's my favourite tank. ( I have many tanks and rdas in circulation but always come back to the baby)