Unvented hot water cylinder

aetbaar

I am getting quotes for a new boiler and hot water cylinder

I was initially going for the Haetrae Megaflow unvented cylinder bit was made aware that there are many other makes out there that are just as good at a cheaper price

has anyone had any experience of these

my plumber mentioned joule but there are many others like main, telford, gledhill, santon, greenstore etc

The joule has a 25 year warranty and is also duplex stainless steel like the megaflow ones

i just wanted to see if anyone had any experience of one in particular and whether quality on these are usually as good as the Megaflow

also i am going for a vaillant system boiler - and undecided between the 30kw or 37kw 630 vs 637

I have a 5 bed detached house with two bathrooms and about 15 radiators _ i want something that would also allow for a loft conversion in future - my plumber says the 630 is ample but wandering whether i should go for the 637 37kw or whether that is just a waste of time

finally for four of us i assume a tank size of 210 is ample?

thanks