I think parts compare favourably price wise, and they are just as good as any main brand boiler in component selection, that is you find parts in there which look very familiar when you are used to working on more expensive boilers. Easy to work on, have a lot of diagnostics on board, some of which are inaccessible in the UK but could be made accessible in the future. There are no known major faults. Like all boilers some things are niggly, if your installer leaves flux in his pipes the hot water flow switch will need cleaning before use, same if the water board do work on the victorian system and debris gets through, the fault is it gets stuck on hot water mode return pipe gets too hot to touch and boiler locks out. Very easy to diagnose and fix. Not the boilers fault. The diverter valve is as used by many other makes but has one advantage that it is orientated vertically so that the gland seal at the end where the motor hjead fits doesn't get damaged with magnetight and hence less nuisance leaks from it. You can band about the good ways one manufacturer does one thing over another and vice versa but value for money, go for it.
I was also pleasantly surprised at the good component selection Heatline use these days (anopther B and Q boiler). I am not sure which I would pick, probably Biasi on present knowledge but I could be wrong.