I'd say they're least useful in blitz because:
1) At lower levels, most sailors are not very effective.
2) Small caliber guns don't kill crew.

With the nature of CAs and BBs these days, maybe one
in ten will have guns equipped capable of killing crew.

It's a sell strategy of open market.

They are currently neuts but when a buyer specifies an order like "I want this neut to
be a Sonarman, in the UK nation" or something along those lines, then the seller
converts them to support class of the UK and then trades them in.

Essentially, this means spending a few points for conversion so you might actually
need to have points to sell as well as credits to a seller who sells neuts to
compensates this; sometimes they don't ask for them, points hardly matter anyway
outside rolling sailors.

@Topic starter

Certain people 'Brushed me off' saying 15 Potential sailors are 'no big deal; so what?
Hahahaha! ROFL!'

I'm not going to tell you that though, TBH I think +15 potents are more useful to you
than selling but if you need the creds, Planes and Sonarmen are your best bet.

Medics are usually the highest candidate because of crew death back then in CVs but
that's gone now due to the recent CV patch. Note however that they only eliminated
crew death on Vets in pilots from being shot down by AA, AAW and Fighters; they can
still die from an enemy BB shell but that's like once in a blue moon. I'm not sure if the
same applies from bomber attacks on your CV.

Still, medics are not entirely useless, it might actually be more useful now in blitz
though to save up on precious expert gains as the mortality rate for your crew in DDs
seems to be high here but again, this becomes limited use and you might want that
support slot to level sailors too.

Seaman is an enigma, although most people will want this guy for reps, restore and
fighter--who? You guessed it right, CVs.

Neuts are not tradable? i see them selling all the time on the trade and barter
forums though.

Eventually, all BO's will overshoot their guildelines once they get to higher levels with
decent experts/vets (then you'll eventually skeletonize them), so a +15 isn't necessary.
You can't sell BO's, either.

You could class him as another class and sell him, though (planesman/sonarman: read up on
medics/seaman).

You cant sell a neutral or a BO so you are either gonna keep him, dismiss him, or
class him as something else to sell him.