Schacht were rather low budget - which does not mean that much optically (they made mostly Tessar clones and other rather basic but quality designs, with good glass and a good formula), but mechanically, most of their lenses are not up to particularly high standards.
Worse for Leica users is that most of their M39 lenses may have been Paxette lenses or for other obscure German cameras (Leidolf?) with a different register distance and rangefinder scaling. LTM Travenars do exist, at least for the Periflex, but given the poor reception LTM Travenars generally get (which is much worse than to be expected from the Paxette or their SLR lenses), I suspect that most of those sold on ebay and camera fairs are either in straightforward Paxette or similar mounts, or were poorly converted.