So, I've just been trying out Music Label 2006, and here's what I can tell just based on a few minutes of experimentation.
While Music Label is much more polished than MP3 Collector, I don't think it has nearly the feature set of collectorz. Overall, ML does much more than just catalog mp3 files--it also does regular cd's and has a loan manager for lending out cd's, and some other extra features. Actually, if you're familiar at all with my reviews, you'll know that I don't like it when a software tries to do more than what it was initially meant for. So ML has a lot of extra features, but it doesn't have the capability to do what MP3 Collector can do as it strictly relates to mp3 cataloging. One thing I noticed right off the bat was the importing capabilities of Music Label...not that great. Sure, it imports the tags of the mp3 files, but if you try out MP3 collector's import routine, you will see how much insanely more powerful it is (I won't go into all the detail).
One thing I like about collectorz software is how they have separate software for mp3's and another one for cd albums (Music Collector). Their philosophy behind it (and I agree) is that albums are a cohesive unit of songs, whereas mp3's are individual files (even if you can have several mp3's from the same album). the point is that they need to be catalogued differently, and it would be difficult to mix the two mediums in a way that maximizes both of their characteristics. Because of this separation of software, I believe collectorz has more ability to include more powerful and extensive features than Music Label.
Anyway, that's my real quick review of it. Sorry, Dr. Leech, but I think MP3 Collector is the best as far as cataloging mp3's, especially if you have them on many cd's instead of the hard drive. I haven't seen another software come even close to it. The speed issue...well, personally, I just suck it up because I haven't found anything close. However, I used to be active on their forums...sometime, I'll go back and ask them what is the reason for the slow speed and if there is anything they could do to improve it. In the past, they have been very responsive to user suggestions.