The Vegas Stabiliser may be an old version but it works extremely well and is so easy to use compared to Mercalli V4. See this quick test Mercalli leaves a vertical jitter which the CMOS fixer is needed to remove. I wonder why they dont combine the two? The result of both together is then a little better than Vegas I think on this test.
I seem to remember reading somewhere that Sony Stabilize is actually Mercalli V2. In any case, I found Mercalli v4 to be faster and better in - almost - all cases, but it can also be a bit finicky.
What I found:
Very important to set your project frame rate to be identical to your media frame rate.
Spending a lot of time fiddling with the settings rarely improves things. I usually just apply the default mode, and maybe reduce the "Pan shot smoothing" and/or "roll compensate" settings for particularly difficult fixes.
If you see jittery footage, something is wrong. Maybe frame rate mistmatch, or sometime you just need to delete and re-apply the effect.
ProDAD recommend applying CMOS Fixr prior to Mercalli, but I find it often works better the other way around.
Lastly, constant re-analyzing can drive you crazy and is a huge waste of time. Either do ALL your edits before applying Mecalli or do a render-replace with a decent intermediate.