On the upside - some of the winning features:
1) I easily added a new "Product Type" (which I simply called "Features") and then added a number of new descriptive attributes (as drop down lists with multi-selection if desired, free text, dates etc) to each "Product". This allowed a significant number of extra and searchable (filterable) attributes for each of my products (items in my catalogue).
2) Adequate multi-language support - that meant I could (and did) change every reference of the word "Product" to "Release" by simply changing one file - and this is reflected in both the user and admin interfaces. I also changed "SKU" to a more friendly "Release ID" (and published it - see below).
On the downside.... it's a little hard to customise the user interface as there is:
1) extensive use of inline styles (I repaced those when I needed to) and
2) inconsistent coding for some of the modules (they were written outside the original project and tacked on 'as is' I suspect).
The impact of that was that when hacking, I got used to the way the core product had been coded and then found that I had to (a) look in a totally different part of the site and (b) adapt to a whole different way of coding to make the change ("featured products" being the an example).
But hey! What should I expect for nothing?
(Hint, in the absence of a easily found Component / Module to -> backend file map, I went into english.php to find the language variable and then used Grep to find where that was referenced in the site files.)
Anyone who's worked in application development (corporate or for yourself) can atest that creating something with anywhere near this level of functionality takes hours (and hours and hours).
I should point out that I do not expect to take any upgrades for this product. I've left the core Joomla well alone but I've hacked this to the point where this will be the only release I use on this site (other than my own future customisations of course).
For the next site, I'll take the latest release and, using the experience I've gained in the last few days, do it again but hopefully a bit quicker and/or better....
Listen to that!! "The last few days" - that's all it's taken to get something pretty decent up and running and it's my first attempt at a Joomla site.
Many thanks to the people who've created this. If I ever make a dollar or two profit I'll send a bit your way.