Gok Wan @ Sainsburys sizes

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I was looking at some Gok Wan cami vest shapewear t'other day ( 3 for £20, one each black/white/nude)

Anyone wear them? Are they worth the money?
Are they long enough?
Does the thin strap dig in?

I'm an average 5'5" and a 14 top half in most clothes.
What size would I be (they are S/M/L/XL not given sizes)

They always seem to be in store so I'm guessing they're a popular staple?
(Might wait till the next 25% off though......)

TIA

Bump -
there must be a Gok Fan out there.......................................

I'm 5ft 7 size 10 and I bought the large - but I didn't get on with them - they kept riding up.