I have a McLeod internal release bearing on my Pantera, and a Tilton unit in my 427 Cobra. For years Dennis Quella of Pantera Performance Center touted the virtues of these units, and I literally bought into them. I have had one failure with the Cobra, and none yet with the Pantera (after about 5000 miles), although stories of failures are rather common.
Were I to do it all over again, I would DEFINITELY opt for an external slave cylinder setup. The actual advantages of an internal unit seem to be minimal, while the liabilities are quite great. For ease of maintenance, and reliability, you can't beat the simple external setup. And when you factor in the high cost of the internal units, it's a no-brainer IMHO....