Used rigid heddle loom

Overview of my experience: owned a Union 36 floor loom, so have experience in making rugs. However, due to some neck issues and strength, I found that too strenuous, so sold the loom. I've found my weaving desire hasn't stopped, so am looking to purchase a loom and I'm thinking a rigid heddle. I have a cheap Mickey Mouse loom that most likely was a child's, but works and is the same design as a rigid heddle. It is very flimsy, with less than desireable features, ie: a length of rubber like a screen spline holds the threads in place.

I have a few questions I'd like answered in making a decision to purchase a "real" loom. On a rigid heddle, what is the minimum and maximum types of warp and weft. Smaller than knitting type yarn, or will it accept larger? Could you give some examples. And the end pieces that take up the weaving, are they easily tightened and loosened. The one I'm using is just wing nuts which loosen as you weave, so forever I am tightening.