Notwithstanding these are for domestic use only they don't have two power supplies for sounders so wouldn't comply with the Health & Safety (Safety Signs & Signals) Regulations 1996 where any audible device used as a fire alarm must have a secondary power source.
If you need detection it needs to be part of the Part 1 commercial fire alarm system installed to the premises, at a stretch for small premises where a detector is required for an inner room only (not alerting the whole building) a Part 6 Grade D (mains & back up) domestic smoke alarm can sometimes be justified as meeting the functional requirements of the legislation even though it's outside the scope of the standard covering it and the purpose it was made for.
Just because someone won't pay for something doesn't mean they should water down their precautions beyond a tolerable level.
Kitchens should usually use heat - otherwise it may go off all the time and end up removed. It might have an exit in it, but you still have to take account of the impact of false alarms. Also I'd be worried if it was my only escape route through a risk room (although microwave and kettle aren't the same as a commercial kitchen and frying range, but that isn't to say they are zero risk in comparison)
