As a basic guide to Airfix kits, those first released from around the late 1970's up to the early to mid 1990's, are generally good, although by today's expectations, perhaps not as 'high tec' as some more recent kits, which is to be expected. Therer are a couple of exceptions, where overall the kit might be good, but can have a fit issue or similar problem (see my Bucanneer!!!). Prior to the above dates, the greater majority of Airfix kits were first released in the early to late 1950's, the 1960's and early 1970's, using, in most cases, the technology of the '50's, which was the norm across the model-production world, and the reason that these same kits, re-released now, are often castigated.
After around the early 90's, having acquired Heller, there was some re-boxing of the latter's kits, and also some Airfix kts manufactured, in France, by Heller, on behalf of the parent company. There was also re-boxing of other companies kits, such as Arri etc.
It's only in the last couple of years that genuine, new kits have started to appear, made, I believe, wherever gives the best deal! Unfortunately, the veteran kits which have been around for as long as I have (literally!), have been re-released at today's market prices which, seeing as they are sub-standard compared to current kits from others in general, can be seen as over-priced and poor quality by those who had not experienced what model kits used to be like.