My conclusion after climbing to gold in solo and flex solo

Flex queue is much harder to climb in (solo) than it is in solo.

The match making is awful in the sense that because its using it own MMR you can get matched with and against bronze all the way up to diamond players once you hit silver. Stomps occur much more frequent and harder because of this. Premades make trying to snowball as a solo player much harder. You can expect 3 even 4 man ganks on your ass. If you thought you saw troll, cheesy, or really off meta picks in solo than your going to love flex. There are 2 type of high elo players you will encounter. The ones that tryhard and the ones who play whatever and treat flex likes its normals. Unfortunately you will encounter the latter way way more.

If your willing to swallow your pride and dignity then climbing it with a premade will make it easier if you are all at least gold elo. If your trying to climb solo then you will have to be able match the skill of potentially diamond players. If your lucky they will be playing like a filthy casual and you can hopefully take advantage of that. If they are the latter then hope your good enough not to feed them. If you get the former on your team, ping them back when you see them doing something that seems like a horrible idea (because they will and very likely throw the game or ruin your lead). Don't be afraid to dodge if you get matched with a premade that hell bent on playing the most borderline troll comps/picks. The only roles I think you can get away with playing something aggro is in top and jg. Just make sure if its top that your escapes/mobility is good enough otherwise your just going to get CC and/or bursted to death if you step out line in top.

Only did it for the reward, so now I can rest easy not having to touch that nightmare of a queue for solo players.