Has anyone used Testors decal paper? If so, what is your take on it?

I use it all time for my decals, white and clear. Works great. I haven't tried any other brands and probably won't inless they're available at a hobby store

Sealing the print is the tricky part

I am new with this--what is involved in 'sealing the print'?

Sealing means spraying the decal sheet with a bonder spray to make the decal waterproof. I have had "acceptable" success with testors ink-jet decal paper, and it is cheap enough that I would recommend anyone who is curious to buy some and experiment. If you are doing dark-colored decals on a white or light-colored background - it works great. Light colors or a dark background are tricky because printers do not print white, and light colors require a white background in order to show up.

You can also get liquid decal film that you brush on, Badger makes it, other might too

I've had good luck with the Testors paper and Testors decal bonder as the sealer. Drawback is it takes some time to allow for all the drying between steps. After printing, you need to wait several hours before spraying the sealer, then have to wait overnight before applying them to the model. It doesn't hurt to print them one evening, spray them the next evening, and apply them the following evening.

Have you tried Micro-Scale Liquid Decal Film? It works pretty well. And it can be used to save old decals ... like the Champ "Reading Company" Dulux Gold Passenger Steam decals that I bought in 1976 ... I floated some on the sheet with an Home Depot disposable foam "brush" and let it dry (I wanted to make sure it would be dry so I did it just before calling it quits for the night.)

When I used the decals a couple of days later, they slid into position just fine. I had been concern about their age -- I had heard horror stories about old decals flling apart and at this point, all of my decals qualify as old.