The main problem with moon clips for .38/.357 cartridges is the irritating fact that there is no standard dimension in the cartridge industry that establishes a case dimension just ahead of the rim. Unlike semiautomatic cases which have an extractor groove of a specific dimension, the straight wall .357/.38 cases either lack a groove or have one designed by the manufacturer. SAAMI does not address it as far as I recall.
Hence I have spent a lot of $ trying to find the right size clips for each of the various brands of ammo. The SLITS seem to have eliminated this problem but I have not yet tried every brand of ammo in my stock. These clips loaded much easier for me and they allow a bit of spring just where it’s needed to accommodate minor cartridge dimensional deviations. They probably won’t work with Russian steel case .38s since those have no groove whatever. It is not hard for me to avoid Russian ammo so that won’t be a problem for me.