That penalty charge would be enough to make me stick to more conventional means of payment, just in case of an accidental breach of the conditions.
The risk does seem to be increasingly out of proportion to the benefits; you only really save money if you make open jaw, or single leg journeys, and then only if the open jaws are on different routes. Going to Weston and back from Yatton comes in at a return to Weston if all off peak, or 1.70 saved if the Weston journey is in the peak. For me, adding Swindon & the Kemble line has rather marginal benefits, so widening the area is increasing the possible risk without any real likelihood that I will travel to the Kemble line. The fares themselves are getting to the level where you think about the journey rather than just treating it as casual circulation around the local area. Weston to Kemble anytime return is £105.00! The highest fare on the previous area was probably Weston to Chippenham at £82.40, so I suppose we can console ourselves that the uncompleted journey fare remains less than the possible maximum.
The PAYG card may be convenient, but we can buy tickets on the train from Sea Mills (SML), without needing to commit the tap operations to memory. On the other hand, the original stimulus for getting a PAYG card was discovering, on the return journey, that I had been issued a CHILD ticket.
On the plus side, the PAYG email telling you that you have been charged now says how much.
I had another case of the taps coming in late recently, but fortunately it went into autocomplete mode, and as the journey was correct I did not try amending it. Five days later when the taps came in the whole thing was revised. This is what it should have done with an incomplete journey accusation, including removing the customer input taps, which would have avoided the problem I described above. Starting by going into autocomplete mode would also have been better. There is very little evidence of careful design in the system.
It is interesting to speculate on what determines the autocomplete. For this case it looks like majority voting, I had made return trips to Severn Beach (SVB) twice in the month, and only once to Yatton, so the fact that I arrived at SML before the Yatton train was outvoted, presumably supported by the return just after the train from SVB.
