I love our Jr, and prefer to use it rather than a 3burner when cooking for just the two of us. I don’t see a big difference in warmup time, perhaps because its cube shape is more thermally efficient than that of the longer 3burners. And, indirect heating in the middle is always present.
What I didn't like about it was that there were no casters *about to be corrected, and the virtual impossibility of raising and lowering the swing table because of propane tank interference (corrected by using the slider setup available on most x000s by the mid 90s. It really wasn't easy to use...
Perhaps this one nonfeature was a big contributor to its discontinuance by Weber so early. Otherwise, it is the only 2burner with 2 rows of flavorizer bars, which I really strongly prefer in my corral.
I have a posting which describes most of what I did with it:
https://tvwbb.com/threads/junior-xxi-progress-documentation.96732/#post-1124064