Just played a mix to test the unlocks
Loch 'N Load is insane vs scouts and on mids, with kritz if you hit it's pretty nutty. You can literally snipe their Medic as a demoman without sticks extremely easily and it just munches on scouts.
Parachute was aids but more gimmicky - if your scouts just shoot the parachuting player its a free pick, but if they don't you can do surprisingly more than I expected.
Gunslinger was frustrating to play against occassionally in scrappy fights but in general was very easy to deal with
Jarate when holding or just spamming it in then pushing is crazy good, easy to just spam it into choke and deny a push and kill everything. Makes playing without Jarate unviable from what I played - same with the old quick fix, you had to use it essentially.
Didn't really notice anything else, sandvich was kind of dumb but I noone used much else than the above. I'd assume rescue ranger would be good but haven't played vs it yet
Edit: Atomizer could theoretically be really strong since you can just dodge the soldier for long enough to kill him but I haven't played soldier vs it yet
Overall, I felt that the Jarate, Rescue Ranger and possibly the
Atomizer were the only very broken unlocks. The others could be easily learnt to counter or were comparable to other weapons available - such as the direct hit and loch n load. The parachute seems strong but giving up a weapon for it makes it more of a gimmick than anything.