Coldkennels
Barnack-toting Brit.
This is interesting, because I've never had an issue with the Alden loaders and either FILCAs or IXMOOs. They're an utter nightmare with Contax and Contax-patterned cassettes (like the Canon and late Leotax ones), but FILCAs close and click into place perfectly. I actually have to put the entire bulk loader into a dark bag to make sure Contax-style cassettes are closed in an Alden.
As an aside, one of the biggest problems with the Prinz one is that while it looks like an Alden, it really doesn't like working with a FILCA - or any dedicated cassette, for that matter. Here's a quick comparison of the Computrol, Prinz, and Alden door-closing mechanisms:
(I can't find my Watsons - I've only just moved house and a lot of stuff is still in boxes!)
Of the three, the Prinz is the worst to use because they placed a flat spring to act as a "clicker" on the serrated wheel that counts the frames loaded right in the way of the cassette chamber. It is a nightmare to get a cassette in and out, and this is even more the case with the slightly larger FILCA - it's a real struggle. Once it's in you then have to make sure the winding crank is fully engaged, as it also doesn't find the right slot every time. However, it will close the FILCA well. Good luck getting it back out, though.
The other two both engage with a FILCA easily and cleanly, but the Alden needs downwards pressure on the locking knob to ensure the FILCA closes. This is seemingly because the knob can be pulled much further up than the Computrol, which actually makes it easier to insert and remove cassettes overall. If you weren't pushing downwards on the knob, I can see why you might be having problems, but other than that, there's no issues.
One last thing, though - note that the yellow Alden has a rectangular slot for a cassette mechanism, while the Prinz in grey and Computrol in red both have round ones. This is because it's the only one of the three that can engage with a Zeiss cassette at all, and the rectangular slot is to accommodate the different closing mechanism. A Contax cassette won't even fit in the other two (they don't have a space for the Zeiss cassette's locator lug) so if you ever plan on using a Zeiss camera, go for the Alden.
