Avantix had it's limited uses but it's major drawback was the software crashing and the fact it couldn't deal with offline transactions.
Avantix MK 2 (the grey ones) is capable of fulfilling ToDs (internet bookings), checking APRS (disabled passengers) bookings and much more. Its all available for train companies to use, but most choose not to as it requires WiFi to function, which of course isn't available on all trains, and where it is provided is subject to the vagarities of the 3G/4G signal to the WiFi kit on the train creating a less than optimal experiance.
Again card transactions can also be authorised online as all the chip & pin variants are capable of having a SIM card fitted, but again most train companies choose not to as signal isn't guaranteed everywhere which of course would prolong card transactions whilst awaiting authorisation.
Avantix can issue all tickets with the exception of those requiring compulsory reservations, seasons longer than a weekly plus Railcards. I think it often gets unfairly slated for reasons that are probably more to due with poor operator training and software restrictions actually put on by the train company limiting its use.
I remember having to lug around a mini fares manual, routing guide, timetable and supplement book along with the weekly engineering circular amongst other things. The Avantix on the other hand enabled me to do away with all of that as it has all the up to date timetables within in, plus all fares between stations. Furthermore it meant that I don't have to manually calculate fares anymore which often weren't in the SPORTIS due its lack of memory.
People also often complain that it is slow, however compared to SPORTIS where you issued tickets first and took payment last, it will always seem slower, however more often than not its finished issuing tickets before the money and change has finished passing hands. Granted the card payment process is a bit of an ache but then again thats been foisted on all retailers by the banking system which in fairness increases card security at the expense of speed.
In some ways I think its a shame that the onboard system of issuing tickets is diversifying, rather than having everyone using the same brand and users pushing for improvements which everyone across all train companies will benefit from. But on the other hand I guess the newer entrants to the market will have to up their game to provide something which is at least as good as, if not better than the competition.