Okay, these things are utterly dissapointing and useless (at least from what I could tell so far).

-Difficult to find (unless you already know where to search)
-Usually in the middle of the level/combart area
-Last only 30 seconds
-Only a meager, difficult to smoothly pull off, jump

Now let's combine all these into a couple of scenarios:

Scenario 1. You don't know where the boots are.
You enter a level for the first time. You spend a few minutes shooting all the things (maybe even hitting some of the enemies) until everyone is dead. Only then you can try looking for secrets (usually very out-of-the-way), and you find these boots! Cool! Oh, they last only 30 seconds? Better get to the next part of the map where there are enemies! Alright, enemies on all sides, got 10 seconds left, how the frick do I use these things anyway? Time's out. And you're probably dead because you were messing around with the boots.

Scenario 2. You know where the boots are.
You immediatelly dash for them, loosing a lot of health in the progress of that. You enter the secret area by taking some more damage (cuz the enemies be shooting and stuff). You get the boots, but you still don't have much use of them since the jumps are not that great. So you wasted your time and armour and HP for basically a cosmetic thing that doesn't last very long anyway.

Ways to fix the problem with the boots:
-After acquiring them, you have them till the end of the level.
-Instead of a double jump, you have a long jump (half-life style or jetpack style)
-They're not placed in a secret area, but instead are in specific points throughout the regular map
-There's way more of them around

tl;dr: The boots, as they are now, suck ass. Please fix them.

P.S.: Maybe I'm just an idiot that doesn't know how to use them proper. Feel free to let me know how much I suck.

The boots respawn after the 30 seconds, so you can use them as many times as you want. Usually I'll clear an area first, and then see what I can do with the boots at my leisure.