I don't get why an unvented is being recomemended.
Because the OP isn't happy with the poor performance from a combi when more than one hot water outlets is used. That is why an unvented is then being recommended.If more than 1 hot tap is open at a time it is really poor
This thread is all about a badly performing shower and not being happy with the prospect that a combi can really only supply one outlet properly at a time.