What is the draw back

if I run mini spools in my 9" compared to a posi? Street driven only.

Mini spool will lock both axles same as a spool so it will make it harder on axles and front tires when turning also the mini spool is held in place by the spider gear crosspin and it will wear on it quicly and eventually break the pin. IMO i wiuldnt run a mini spool ever either a full spool or a posi unit.

Thanks no mini spools for me.

How much street driving are you going to do? I ran a welded spider gear deal for about 10 years before it broke. I popped in new side gears and a mini spool and it has been in there since. My Pinto is a street car and hardly ever went to the track.

As far as drawback eventually you will break a side gear or twist the splines on your axle. How long it will take depends on car weight, tire size etc. Twenty years ago before rearend parts were plenty and cheap lots of people did it.