If you are talking about the original Borg-Warner 1305/1339 Quadratrac found in 73-79 Jeeps, it is a good system for what it was designed for. Roger Mears ran a J10 rally truck in the late 70s in the Baja races behind a 500hp 360 so they can take a lot of power. I have one in my 73 J4000 and it has never let me down and is the best 4wd for snow in my opinion.
The QTs got a bad rap since they do need to be operated and maintained properly and a lot of owners didn't do this. The case takes a special fluid which is basically a 30W motor oil with a limited slip additive for the "clutch cones" inside the case to do their job which is to send torque to the front or rear axle depending on which one is slipping. Another feature is the emergency drive which is a vacuum shifter to lock the front and rear driveshafts together bypassing the cones and putting equal power front and rear. This cannot be used on hard surfaces or where there is a lot of traction. I have had maybe 5 or 6 opportunities where I had to use the e-drive and I've owned my truck for over 10 years. People think they can just lock it in e-drive and go and end up breaking components. The drive chain is another source of problems. It needs to be checked periodically to see if it has stretched. I do this once a year along with a fluid change and the first chain in my truck went almost 100k miles. When the chain stretches, it will skip on the drive sprockets inside the case damaging them and eventually the chain may break which tends to grenade the case.
New parts for the QTs are getting tougher to find as time goes on but enough of these were made that there are lots of donors out there. If you are looking at a vehicle with a QT, don't base your decision just based on that fact. If the rest of the vehicle is a rat trap, then the QT is probably toast. But if it is a well-maintained vehicle then chances are the QT is in good shape.
73 Jeep J4000 360 .040 over, Summit K8600 Cam, Edelbrock Manifold and 750CFM 4V TH400/1339 QT
78 Cherokee Chief- Hunting Property Rig
05 Grand Cherokee- 3.7 V6 5 speed auto