Unfortunately there really hasn't been any updates for that software for a long time. You could try the usearch61 (alternatively vsearch as a plugin) approach as another method, as it's a bit newer.
Another option would be one of the ways that was done a long time ago-filter out rare OTUs (normally PCR-based chimeras would be low frequency), and for any OTU that of interest, e.g., one that's significantly different in abundance, take the representative sequence from the rep_set.fna file and blast different fragments of it (e.g. 3 different 100 base pairs of it) and confirm that the different fragments all hit the same taxa. Sometimes there are multiple taxa hit at high % identity, and that's fine, as long as two of the fragments aren't unambiguously hitting different taxa.