I'm presently using the Perfect Multi-Gym bar at home: But the Crossgrips look like a nice alternative for travel.
I don't like the idea of hanging on to towels as though they were ropes. I think this is better and more stable: I've tried this approach in the past and it worked reasonably well. I put door stops under the door on both sides and at both ends to ensure that I would not damage the hinges. It would do in a pinch. But I prefer to hold on to a bar.
I was thinking yesterday at my weight I'd just ruin the door hinge/lock even with a closed door, the shim is a good idea.
A direct comparison between the portable CrossGrips and the Perfect Multi-Gym: He mentioned that the Perfect bar might cause some doorframe damage. I place sponges between the bar's pads and the vertical part of the doorframe where they press, and have had no damage since the start of the pandemic. He also complains a bit about the cost of the CrossGrips, which are are presently $119 in the US. Meanwhile, on amazon.ca they are CDN$226.84! I don't need them presently, but I do see myself buying CrossGrips at some point in the future.
Apart from the free power drill you get with the $10 pullup bar, I still prefer my Perfect Multi-Gym bar. You don't have to retrofit it with extraneous materials to make it work on your doorway, because it is adjustable. Also, the pads that press against the vertical part of the door frame are flat and less likely to cause any harm to the finish. And I was wondering about his claim that he would do muscle ups on the doorway bar.