The handle extensions don’t really get in the way when you have a UPD. I’ve never had a problem with getting tripped or hit by my handle. The only time it’s a problem is if you UPD at low speed while trying to execute a turn. In that case your direction of momentum and the direction of momentum of the unicycle can be such that the handle extension might trip you or hit you in the leg. But it’s never been a problem for me.
Most UPDs are off the front of the unicycle at jogging speed or faster. In those cases you go sailing over the handle and the unicycle simply falls to the ground while still traveling in a straight line. When you UPD your instinct will be to push the unicycle down and that works in your favor.
If you build up the handle so it is extra wide or otherwise more bulky then you can have more problems. As long as you build the handle to be narrow you shouldn’t have a problem.