For it's intended purpose, it works quite well, although the demo version leaves an annoying message on the upper left of the joined clips (which the readme file fails to tell me about), but if you plan on using a large enough letterbox on your whole project, it shouldn't be an annoyance in the end as it will cover it up.
The program lives up to it's name however, I think the program should also have an auto-split option if you attempt to join clips and it adds up to something larger than 9:57 minutes (or 9:27 for PAL).
The help document on the author's website is rather informative and easy to follow. And for a plugin like this one, I suppose 7 bucks isn't bad. It seems to be worth it, actually.
Lastly, the program was stable when I was using it.