Hi Kevin,
Robert makes some very good points regarding nibs, etc.
As far as prices of pens go, 63 pounds is not a bad price at all for an M250 in Europe, as it equates to about $ 105 or thereabouts. Especially if you factor in shipping costs and Customs and Excise for a pen to reach the UK mainland from outside the EU, which adds an amount for shipping plus an additional 24% C&E in the UK, if I am not mistaken.
Regarding the M vs the F nib: ask yourself what nib you normally write with and like to write with. If that is an M, it is probably worthwhile ordering an M and waiting for an M, if that is possible of course. If your standard style is an F, go for the F.
In contrast with most modern manufacturers, Pel nibs write narrower in gold than in steel, at least in my experience, but then, the steel nibs are really a little on the wide side.
Regarding flexibility: a modern Pel nib is not really flexible. It just isn't a nail, like many Waterman nibs, so yes, you get a little line variation, but really only very little. And you won't get more from a standard F nib in this case than you would from an M nib. As Robert indicates, it would indeed feel like a smoother writing experience than with an F nib.
If you are interested in trying any bespoke nibs, just give me a holler back channel (use the email button on this message) and I might be able to help you out. I live in the EU

, so that would save you at least some hassle.
If you do have a 28 day exchange policy, you may want to see whether you like the F nib, but please do make sure that you are allowed to use the pen in that time. With some warranties if you use the pen, you lose the right to exchange, too. Better check on that first.
Anyway, HTH, warm regards, Wim