Certainly the best advice. When I asked a long time shooter and handloader about this many years ago, he told me the same thing. He was right but I didn't listen. I ended up buying not one, but two Colt Conversion units several years apart. One had it's own frame, a Colt. Seems like the other I only used on a Colt frame. I tried a varierty of ammo; CCI SV shot better than anything else, but I could hardly call either conversion unit accurate. A cheap .22 pistol would do better.
I've read where some of the other conversion units were accurate. They may be.