hassle? Not really, the OD just needs tuning like a new carb or anything else. I'm very happy with mine - off the line like a 4.30 gear with the low 1/2 set and down the road at 2.68 + lockup. It's both a performance and economy upgrade in 1 tidy package.
Mine was done by Tranztech in Dubuque, Ia, quite reasonably for a turn key job.