Opinions Sought: 50 Cal conversion kits

I'm out here in the "Land Of Fruits And Nuts" also known as California.

Our son of a Nazi governor, Arnold Swarzenegger, passed a law several years ago that prohibits the ownership or transfer of .50 caliber rifles in this state. So, my dream of owning a Barrett went out the window.

Unless I win the Lottery and can move to Kentucky to this place outside Liberty. It comes with a transferable Class III!

I should have bought one of the Ma Deuce kits that SARCO was selling about 10 years ago. It would have made a nice big brother to my M1919-A6.

The good news is they're selling M60 kits, but I don't have money for toys like that anymore.

Anyway,

Here's the question to all you shootists out there. There are several manufacturers building kits like this that are a drop on 50 cal upper for your M16/AR15 style lower. It looks like junior and his ilk missed these items when they enacted the law here in California, so I'm pretty sure I can get one.

Have any of you had any experience with these things? Are they worth the money? Does it destroy the lower (I've heard stories about lowers cracking due to some weird resonance. I don't know if they're true or just scare tactics. Some say it only happens on cast lowers and not forged)? If I get one, am I better off springing for another forged AR lower?

Thanks for any and all opinions.