I've been using Fab for about a week or so now as my primary provider. I have used Vader and Smoothstreams too so I think I can compare properly!
I will start off with quality . The quality is great. Most channels work fine usually (Willow seems to be having an issue though). The one really annoying issue I have had is that the American/Canadian channels especially the ones with "E" on top seems to have a slight stutter. A lot of people won't notice this but I do and it's kind of annoying to me, however as of yet it's not really a deal breaker. If not for this issue, the service would be perfect.
EDIT : Looks like they are replacing a lot of those "E" branded channels with better sources with no stuttering. This just makes it a lot better!!
The EPG is great. Works fine on Dreamlink(DOL does have it's EPG related bugs independent of the provider though)and Kodi as well as Perfect Player.
Where they really shine is the customer service. Almost everytime I have opened a ticket or posted on the FB group, I have had instant response.
Another really really cool feature (the main reason I went with them) is the ability to change mac address myself. What's even cooler is you can use it on Kodi/Perfect Player using their add-on and an M3U8 file and have a mac address registered as well to use on STB.This is really important to me because often I am at my girlfriend's place and the ability to login to another device is a great thing.
I can't comment on the VOD much because I haven't used it much but from what I have seen, it is behind the competition and they do need to up their VOD game.
The biggest complain I have is that for some reason using it on Kodi loads the VOD too on the PVR client and the only way to avoid that is to have them remove the VOD content altogether . I wish they could work something out about this because Vaderstreams has VOD too but won't populate the PVR client .
Overall, I am happy with the service. I plan on sticking with them. The price is unbeatable and for the price the small issues I have is acceptable.
Im with Flawless and Vader. Flawless are the best for the UK channels IMHO Fab use the same US/CA E channels as Flawless and they arent good. Vader have excellent US/CA channels when up.