I had a set of SoLows on my 5 1/2" Mk II. They were OK, but as you had to remove the rear sight and epoxy them in, you couldn't switch between dot and irons on the fly. And if you don't use the epoxy to glue them to the receiver, they do move around (getting the epoxy off without scratching the receiver is tough-acetone did not soften it as they claim). Using the epoxy is necessary because they use steel screws threaded into aluminum bodies and you can't generate enough clamping pressure to keep them set. Plus, they're not something you take on and off too many times before the aluminum threads strip out.
Reddot goes on the fritz? Rings come off. Scrape epoxy off receiver and rings and do it again.
Position of the rings is limited by the rear sight dovetail and position of the ejection port, you DO NOT have any flexibility in the placement of the rings.
Make sure you mount the receiver to the frame before the epoxy hardens, as you're mounting these on a round receiver with no point of reference, they can go on crooked and make it impossible for you to get the two back together. Also, dry fit them first because mine required filing of the fingers before the frame would mate back up to the receiver.
There was lots of discussion on the old Mk II forum about these things. Unfortunately there is no search function, but you may be able to find other comments by browsing around:
http://www.network54.com/Hide/Forum/52578?it=0
They were better than drilling and tapping the receiver. Barely. But given the choice, I'll choose a proper mount.