The Scarab I use has been on 2 month long caving expeditions with hi wear conditions and it has also endured similar conditions at home. It is approaching 2 years old now, and has seen some pretty tough vertical caves.I will have to retire it soon as the bar is finally getting close to wearing through.
My two cents:
I have found it to be an acceptable alternative to other descenders (Stop, Simple, Rack, etc) on European style rigging. It is easy to use. Much faster change over times than a rack. Slightly more simple than a Stop and easy to lock off. Heat buildup is fine on longer drops (+30m) if the rope is wet, but can get very hot on dry rope which requires a slower descent rate to allow heat to disperse. A good idea no matter what device you use.
I will buy another one to have in my collection. With big long drops, the rack is still my preference. However, I tend to be in caves where single drops rarely exceed 100m without hitting a rebelay so the Scarab or Stop work just fine.
Safety Cons: It is possible to catch the gate of the carabiner with one of the horns when you go to load weight onto the device. I could see it being a major problem if you shock loaded it like that.
Note: Never use Figure 8's (IMO) for caving. Especially on long drops, they twist the rope too much and have stripped the outer sheath off new ropes (172m freehang). Even on short drops of 15 meters Figure 8's generate some nasty Spaghetti piles, leading to some pretty horrible rebelay conditions.....