I will simply copy and paste my comment from their support board - because having looked at the source code, copying and pasting is something they're happy to inflict on you.
This was after 3 weeks of trying to get the thing to work, trying to work around the fact that documented template over-rides don't work, and when implemented simply cause WordPress to crash.
It turns out ...[category listing]... is not the only template that doesn't allow over-riding. I spent about three weeks trying to get the Business Directory to work the way I had specified to my client that it would work. Here's a brief outline:
contains a search form which searches all fields without having to specify the field, but user CAN specify which category / categories of business they wish to search. Your module doesn't support this and doesn't seem able to do so, which is a pity as it means I can't use it.
contains a compact list of businesses showing only a few fields - either a search result or (default) just one of the categories. Your module doesn't support this and doesn't seem able to do so, which is a pity as it means I can't use it.
clicking a listing opens it in a modal box - your module can do this (as long as I add in the suitable JQuery) however since the two items above are deal breakers, I didn't get this far. Modal box also contains a Google Map (pity - I'd have bought the module) and region search (for which I'd have bought the module) and a zip / postal code search (for which I'd have bought the module).
However since those other items are deal breakers the modules I might have bought are academic.
Template files that don't always work ...[is not the only problem].
A plugin where the template calls a method which is basically a wrapper method for another method which is basically a wrapper method for another method which is basically a wrapper method for another method which is basically calling something straight out of your API which can't be over-ridden and forces the user to have their installation work your way, is frankly a pain in the neck. I had to over-ride so many of your methods I may as well have written the thing from scratch. You make so many database and file calls it slows a decent system to a crawl. You have a folder called "views" which contains a controller which accesses a database (so that'd be the model?). Is that a deliberate anti-pattern?
I realise it's your module, you do it how you like. I realise that conventions in programming are just that - conventions, you don't HAVE to stick to them. But I really think a little bit of DRY would go an awful long way in what should be an incredibly simple plugin to build. So I can only think you made it so hard to work with to force people either to buy modules or hire you to do custom coding.
The problem is - I would NEVER pay for code that is this badly designed. I realise some of this is down to the awful code design of WordPress (not graphic design - it looks lovely - I'm not saying it doesn't - but under the hood WordPress isn't well built). But some of it is down to additional layers of complexity you've added which have made life a hideous mess for me for the last three weeks and probably lost me a major client. So, not only would I never pay for code like this, I now can't pay for it. Or my rent. Thanks guys.
I'll find a different plugin...