Both the units performed OK - nothing particularly spectacular. The U500 certainly performed better than the T100, so it gets the nod for consistent and clear playback (with all the warnings and caveats about using the mobile antenna).
The T100 isn't advertised as being compatible with XP MCE2005, which is a limitation for a card-based TV tuner. It does come with a Microsoft BDA driver though (Broadcast Driver Architecture), which should get it over the line. The flaky performance is a worry, however. You'd want to be very confident in your signal strength, given that the T100 seems liable to exhibit degraded performance at the drop of a hat.
As nice as the ComproDTV2 software is, it's not really suitable as the basis for an HTPC - the feature set is fine but it doesn't really integrate with anything else other than ComproDVD2. You really want any TV tuner to be fully compatible with a complete HTPC package like MCE or MediaPortal.
More worryingly is that you can't find any reference to the T100 on Compro's Support site. There are no updated drivers available for download - the nearest products are the T200 and T300. These drivers do work for the T100, but you can't help but get the impression that Compro isn't taking this particular product any further.
The U500 performed well, and IS MCE2005 compatible, but it seems strange to use an external USB device as the main capture device in an HTPC unit. It really is much more suited to computers on the move (notebooks) - and considering that that's how it's advertised, it's not such a bad thing!
So I'd have to state that although these products are fine standalone products (with the U500 clearly outperforming the T100), neither of them would sit well in a home theatre environment. For casual, ad-hoc TV watching on a non-dedicated system, the U500 is an excellent choice.
Compro VideoMate T100
S-Video/composite video capture
Lack of ongoing support
Rating - 5 out of 10
Compro VideoMate U500
Stable and consistent performance
Mobile antenna not guaranteed to offer reliable signal
Not an appropriate format for an HTPC
Rating - 7 out of 10