We use Manners Minders in our kennels at work, they're incredibly useful for getting your reinforcement timing and placement right.
They do jam a lot, we just had to find the right size kibble to put in them. Too big: jams. Too small: jams. Soft treats absolutely do not work, crumbs are a very bad thing! You might try getting some free samples of different foods to figure out which one works best.
When you push the remote to give a treat, the Manners Minder beeps, which you should be able to hear from another room. When it gets jammed, it makes a different (louder!) beep, which you should definately also hear from another room.