I bought a used 1662 off eBay for cheap, and it has been indispensable for the work I've been doing on a PDP-11. I think the external clock is often a pretty critical feature in being able to sensibly interpret traces. Sophisticated triggering is also very useful for catching a suspected misbehaving chip in the act.
I had considered some of the more modern USB options at the time because it seemed they would be convenient, but in the end I opted for a used old-school tool because it had the features I needed at less actual cost. I have not regretted the decision -- super useful tool! --FritzM.
