Idk
Over the years, I've begun to form the opinion that these 'safety' schemes are nothing but a racket and the tradesmen aren't any better when registered with them than those who are not.
FENSA - I learned after not buying a house 'not all the windows are fensa so they may not be safe' - apparently fensa barely ever turn up to check the work anyway. That was my lawyer telling me that. Windows installed by a non approved fensa person may not be safe.
There's a lot of WTF behind that statement.
(they're British kitemarked, iirc)
Hetas for stoves - bloke turned up and told me that a chimney sweep couldn't have possibly displaced a chimney flue!! Idk if that's true but it seemed very unlikely, and the bloody thing was sticking out of the chimney pot at an angle.
Both napit and the other electrical one - I've had poor electrics in current and previous rental, all electrics were done by people registered with one or the other.
Last I heared napit charge £700 a year to be a member, but I'm entirely unimpresssed with the quality of the electricals in my house, done by someone who put themself on a course just to do this house. Previous house was the other scheme and those electrics were bad too.
It seems to me that these 'safety' organisations earn a lot of money a year to basically be Checkatrade for specific professions, and they're pretty lenient on how much of the work they actually check.
Just my two pennies worth.
DL;DR: I do NOT thing it equals quality/safety
Happy to be corrected by anyone who knows better/has a different opinion, of course.