Just for clarification, I bought Asylum this morning, never having used gamestop downloads or games for windows live before. Impulse is just a downloader, you use it to download and install the game, it is not like steam. Once installed you launch the app itself free from impulse, and it goes through GFWL. I think it also used secuROM to activate, and then I had to input my key again for GFWL.
But that took like 2 minutes and the game works just fine... so I wouldn't let impulse be a deterrent (of course I'd prefer Steam but $4.99 is $4.99).