I can't speak for other RMM platforms, but I work for an MSP that uses N-able, and honestly I think N-able are snake oil salesmen. I get the impression they are a heavily sales-driven company, pushing a poor product and lacking the technical expertise to back it up.
The product has been buggy as hell (we're on version 10). We've had endless issues with scripts/automation policies just failing to run (several known bugs here, apparently), modifying custom services results in them going Misconfigured, services randomly going Stale for no apparent reason (also acknowledged as bugs) plus a LOT of other issues. We generally have 10 - 20 cases open at any one point in time.
Add to that, terrible support technicians with little to no idea of their own product who are extremely defensive and dismissive, attempting to invalidate bugs/problems you report and just generally being quite unhelpful. The turnaround time for us has been 3 - 6 months+ for issues to be resolved, with many problems still ongoing. Escalated cases show that the senior techs, support managers and even developers have little to no idea what they are doing. With some of the bugs we have discovered, I have serious doubts surrounding how (or even if!) they properly QA and regression test their product.
When we raise problems with upper management, they make a poor attempt at going into damage control and come across as duplicitous with extremely poor excuse making, or completely ignore us.
On top of this, I find the web interface clunky, slow (we have experienced many performance issues -- we manage around 5,000 devices) and lacking both power and flexibility. The dashboarding and graphing is extremely primitive and provides little to no value for us. There are not a whole lot of positive things I can say about it as a product. I detailed some of the problems we experienced are here: https://www.reddit.com/r/sysadmin/comments/405xe2/msp_sob_story/cysej7v
Honestly, I'd prefer to roll my own and use a separate monitoring system, and a proper configuration management system like Puppet + PowerShell DSC. The amount of time I've wasted (close to full time) dealing with all the problems with N-able's product would be more than adequate to do this, far more satisfying, and would allow me to fix problems myself far more quickly. Luckily, I'm changing jobs shortly and will be moving back into a development role.