I've been pretty successful using my Smartcard for both weekly seasons and a few returns - I'm just trying out the Flexipass carnet. One thought that I'm not sure how to test, is that I could quite easily see how I might have multiple potentially active "products" on my Smartcard simultaneously (for example, I might have a carnet valid for a month to/from Glasgow, but a weekly season because I know for sure I'll be travelling to/from Glasgow for 5 days that week, plus a return from Glasgow to some other point not covered by either). How will the system know which one I want to use when I touch in at Glasgow Central? Does it wait to see where I touch out, to see if the return ticket was the one I intended to use? If I go back to my home station, and I have a valid season ticket and a carnet will it default to the season? Or will it try to use up one of my carnet of tickets? Given that there's the added complication that the Smartcard can't currently cope with finishing short on the season ticket (which is, of course entirely valid), I can foresee lots of opportunities for glitches and I'm not sure I want to test them at my expense.
I'm not even really sure about whether you need to pedantically touch in and out, especially with the season ticket I have loaded. There are three exits from my home station, but the most convenient one for me doesn't have a reader. At first I kept walking back to the less convenient exit, but then forgot on a few occasions and it didn't seem to matter, I could still touch-in the next morning and get a Journey Started message. The only time it caused a problem was when I wanted to use the season ticket again one evening for a second round-trip to Glasgow - because I hadn't touched out after the first round-trip, when I touched the reader it "completed" my journey but then wouldn't let me touch-in to start the next one, even though that would be perfectly acceptable with a season ticket. I'm guessing there's some sort of timelag requirement between finishing one journey and starting another (unless they've incorrectly set up a feature to restrict seasons to only one round-trip a day), although I can't see the slightest logic as its clearly not a "passback" situation.
So as I say - its actually not bad, and I like the fact that I can buy my tickets in advance given that my home station doesn't even have a TVM let alone a ticket office. But I do wonder how clever the back office systems are for users who aren't just making simple out-and-back journeys using one product at a time.