The main differences are:
- TRMR doesn't use a pin, its just twist and throw
- TRMR safety is just a twist back so its quick to get it to safety.
The end result is that the TRMR is quicker to prepare, load and throw and you can't loose the pin because it doesn't have one. They are a little more expensive but use shotgun caps (super cheap).
Having looked into this with Thunder B's and TRMR's and Ohshiboom's my intention is to get the TRMR. About the only disadvantage I know is its a little less likely to go off on soft ground like in woodland. I made a post asking this only a week ago I think.