Cost – £200 – £300ish – though more if you need a new rim and paying for the wheel build
Weight – Yes, the alfine’s heavy – you’ll be adding anything up to 1kg depending on what you currently have
Spacing – Normal 135mm mtb spacing. You’ll need a tensioner if your frame’s not designed for SS
Durability – I’ve asked this a few times – the answer so far seems to be yes, it’s lasting pretty well even when used for mtbing
Check out the internal gears forum on mtbr.com