I haven't had any issues on the desktop version but haven't used it on the server since we haven't upgraded to a version that has it yet. I haven't done extensive testing but one workflow I had took about 8 minutes to process with AMP disabled and it took less than 60 seconds with it enabled. I'm not sure if this is typical but I've definitely kept it enabled ever since! That workflow was using all local datasources (on my pc). I'm curious to hear if others have done any comparisons.
I've used the multi-row tool several times with AMP and haven't had any issues.
Also, I don't know if this helps in your case but I recently learned that the multi-row tool automatically sorts any columns that have "group by" enabled. I was able to stop using the sort tool before the multi-row in most cases.