Nothing in life is perfect ... but, the Newton plugin works pretty well.
If you own the PRO version, you have a complete physics engine available to you that is already built-in, so you wouldn't depend on any third party plugin.
(I own PRO and still like to work with Newton, but that's just me because I've not always owned PRO)
Having said that, the Newton plugin is not "complete" in terms of where the plugin has progressed to (see the Newton website to see what all has been added over the last 1 1/2 years or so).
I know that an updated version has been worked on for some time [
Ventilator's Post ], but the release date is unknown (as a matter of fact, I don't think that there is any guaranty that it will be completed because the guy working on it has a lot of other things to keep him busy
) ...
So depending on what you actually want to do with Newton, it may or may not be sufficient for your requirements.
Cheers,
Andreas