you pay your money and make your choice.
There are a few airfields that don't allow microlights but many of those that do have a lower landing fee for microlights than for GA types. I did hear that a few folk flying GA versions of aircraft also available as microlights would try to claim microlight landing fees and equally, a few folk flying microlight versions of aircraft also available as GA types would try to bluff their way into non microlight accepting airfields (not me, of course
).
Now most airfields have the internet in their control towers they have G-INFO on and tell you whether you are GA or microlight when you go to pay your landing fee.
It is also worth noting, if you are going to meander across the water, the regulations for France are easier for microlights I believe. The required equipment fit (transponders?) is less in some cases.
If you are not apt to cross the water it may be better for you to look at the many homebuilt GA types and consider joining a syndicate on one. Many will be somewhat cheaper to buy into than a C42.