If you get a PTR without the rail welded on it from the factory, prepare to spend some money mounting glass. You have claw mounts which are expensive (the good ones STANAG) and have a very high mount, but allow for irons and glass. The MFI rail is cheaper and also works but like the welded rail, negates the use if irons without high rings. I've seen MFI's used on MP5s and they work, just locktight them into place and make sure you have a level mount. The MFI is probably your most economical choice. Avoid, the UTG, B-square and other cheapie mounts.