I use to hold an FFL for several years although many moons ago. My department issued S&W model 67's and it seemed like every academy the new troops wanted their own copy of the department gun. For their personal gun, porting was an OK thing to do since department guns could not be altered in any way. I've sent so many guns to Mag-Na-Port for others and myself, I've lost count. After the first 10 guns they gave me a 1/3rd off deal on all subsequent guns I sent them.
In my experience I've found that their porting always helps keeping the barrel down and with recoil and now they're offering many more options that they never did before. When I first started with them they only had single porting for handguns, but now you can get quad porting, dual porting, and rifle porting on your handgun. I wanted them to put their Mag-Na-Port logo on a couple of guns early on and they refused saying that it would confuse and detract from their custom gun business, but now you can get the logo as well.
Currently they are working on three of my guns, all stainless Ruger's. An Alaskan is getting ported and logo-ed, A Super Blackhawk is getting rifle ported and logo-ed, and my 9 1/2" Super Redhawk is getting Mag-Na-Braked and logo-ed. I wouldn't say that you'll get your money back, but it does increase the value of your firearm (unless you decided to port an original early production Colt SAA).
In the end, They do great work and if you chose the right porting for your situation/barrel length etc. you should be very pleased with the outcome. Smithy.