I can't answer the question directly, but why would you expect third party, unpaid software to be more stable than that installed by the makers, who actually designed the package, and have to provide warranty support and meet "fitness for purpose" laws? Open source and third party software can be a great product (some Linux, some Lineage phone firmware, Thunderbird, Firefox etc), but if there were some easy tweak to improve router performance, don't you agree Asus would have already done it?
The main purpose of third party firmware is to make possible new configurations or capabilities that the makers have undoubtedly decided that weren't needed for their target markets, or had unintended risks or consequences. That suits some people, and good for them, but it is a minority. By all means go ahead, but be clear on what you're doing and why you're doing it, and make sure you can revert to the OEM firmware. What's the worst case scenario (possibly a bricked router), and is that an acceptable risk for you?
I don't wish to be rude, but if you're asking in this forum, then perhaps Merlin isn't for you? There is unlikely to be a large mass of customers who both have a VM connection, an Asus router, and running Merlin, and whilst I know that there are some who contribute here, you'd possibly be better off asking in dedicated Merlin forums as to a rounded view of the risks and benefits.
