I contemplated buying the IMTUG myself for my pinkie and ring finger, but then realized why not just use the Trainer for an inverted close for only those two fingers? Thus, I had saved some money.
And, you don't need IMTUG for improving your strength when it comes to grip strength. You need to work on a sensible program with a range of grippers. If you can do 10 nice reps/closes on the #1, you should have the #2.
You could do say 3 or 5 sets of 5 closes of the #1 with one or two negatives on the #2 (and if you cannot fully close it, cheat it closed, then just hold on for dear life until you open it slowly before failure.)
Eventually you'll improve enough to where you can close the #2 for singles, and that will bring you closer to being able to do enough reps on it to prepare for the same procedure on the #2.5 - and so on it goes.
The only reason for me doing extended reps on a gripper would be for endurance, but that's only for grippers below the level I am currently working on or working for.
Right now I am doing 3 sets of 5 parallel closes on the #3 with one or two extended negatives thrown in at the end of the set, and it works very well for me. Going to expand this to 5x5, and then eventually more fuller sweeps, before I start working on the #3.5.