I have been an avid shooter,collector,hunter for over 45 years, and all this talk about devaluing your revolver would be true if it is a "collectors" piece.
I really don't think your 629 will be devalued by magnaporting it.
Unless of course it is a unique factory produced limited production model, in which case I would not do it.
Maybe in fifty years a standard 629 will bring top dollar, but now ???
A gun sent to Magnaport for a professional job will if anything enhance the to someone that understands its value as a shooting aid..you might not sell it to some folks, but Magnaport would not be in business for as long as it has been if it did not work and have some good shooting value or have a ton of happy customers, and repeat customers!
It may not add dollar value/return on investment just as much custom work doesn't, but then what is your point for doing it?
If you want reduced muzzle flip and a slightly reduced recoil feel, go for it.
I have a customized 44 mag. Super Blackhawk with a 5.5" barrel that is a ***** cat to shoot next to a standard model with max hand loads.
If you shoot it without proper hearing protection, yes it is quite a bit louder, I did it once , never again. But remember even without Magnaporting a 44 mag. is hurtful to your ears.
SO I never shoot without good ear plugs, or, electronic muffs .
More muzzle flash has never been a problem for me, because I dont shoot in dark places or at night.
Cleaning is an extra minute more, no big deal.
I fully endorse magnaporting for bigger, hard kicking calibers, I think you will be pleased with the outcome.