Get one of the local fitters who quoted you for a logic + to quote for a vogue. You ll get a 10 year warranty instead of 7 and you won't be paying a monthly subscription for the pleasure like you would with BG. You ll probably pay a local about the same for a vogue as you would BG for a promax. The boilers are worlds apart. The quality of the vogue is superb, a premium boiler. The promax is BGs budget option.
Over the years as you have more call outs to the promax you re monthly premium will increase. With a 7 or 10 year manufacturers warranty it won't, there is no monthly payment.
With a local installer you ll meet the fitter at point of quoting and get a pretty good judgement of him from that. With the big companies it's pot luck who s allocated the job who you get. Don't get me wrong, they have some superb engineers who will do lovely job, but they also have some awful ones.