Super Slow is super stupid. If you try to raise a Deadlift slow, and it might not come off the floor. Move barbells with bad intentions! Push or pull fast! Lift every weight like it's heavy. Produce force. Do more sets or more reps for more time under tension.
On the other hand, only a real clown does violent, explosive 1 rep maxes on the preacher curl. The goal of the exercise is peak contraction, and tension on the muscles. Don't rush it. Isolation exercises on cables, dumbbells or machines (push downs, pull downs, leg curls, calf raises, all manner of curls) with a "guided" path, that you are doing specifically for hypertrophy are good ones to lower slowly, or hold at peak contraction. The weight/reps don't even have to vary too, too much. Just think about the ROM and squeeze, and TUT will increase in a natural, unforced way.
Lastly, you have to consider ligaments and tendons. They progress slower, and need many, many reps to get worked. So why not do high-high reps with low-low weights and long-long TUTs to work them properly?! Think of a boxer, jumping rope for fast feet. Hundreds and hundreds of fast, short, bouncy reps to build up the ligaments and tendons of the feet ankles and get more springy. Or doing 2 x100 band Pushdowns or band leg curls on an off day. 3 sets of 12 wouldn't do shit. You need longer exposure (TUT) to the lighter load.
Figure out what you're trying to do, then use the best weight/speed for that goal. Use a variety of weights, rep/set ranges, speeds or methods of execution. Plan it carefully.