That`s why H&S have us wearing air fed masks now, although expensive for hobbyists it`s your health & up to you. For what it`s worth I used GVS elipse half mask PP3 rated order no 6922G from screwfix in Cambridge the ones with filters on the side, although never tried under a welding mask they were comfortable for my use.is there a special Mask for arc welding, other than a dusk mask.as in breathing fumes
our lads used to use activated carbon half masks P2V disposables when MIG welding aluminium, these: https://www.arco.co.uk/products/1E3000?s=1
They're pricey, though! And IMO there are cheaper masks that will be just as effective. I have used these myself under a welding hood and it works fine.
These days they all have air fed hoods.
Are you thinking of any particular make/model of cheaper mask??