^^^^^Actually 'buying a Bosch' won't 'assure' finding 'assembly string' on a Puro made filter. IME finding assembly string has most to do with the size of the filter. Generally speaking' if' it's still used at all, it will be found on larger/largest application filters. Example, topic filter Bosch equivalent 3323 doesn't use assembly string. Since 08 never seen assembly string on 14610/14612 or any similar Puro made variants. Granted the example shows an anecdotal difference between Puro and Bosch in one application. Wouldn't take for granted that because filter says Bosch on it, assembly string used.
All that said, as it serves no purpose other than an assembly aid, I wouldn't prefer (or not prefer) a filter based on string use.