Over the years I have been beekeeping I have bought bees from most of the suppliers who advertise on the internet , bees from the UK, Germany , Cyprus and elsewhere. I am not able to quantify what differences in temperament /yield etc but so far:
I have not bought a queen whose offspring were really horrible.
All survived their first winter despite my incompetence in early years.
There were no visible signs of any queen or her offspring being incapable of adapting to our local conditions...which can be harsh in winter.
Most local bees - from local stock - are the spawn of Satan being swarmy, unproductive, stingy and generally useless. Of course you may be lucky and your local bees may be pleasant, productive and non swarmy. I read the mantras about "local bees". It is absolute bull excrement as it all depends on the local gene pool..Local bee populations are not homogenous and to present them as the answer to all problems is - in my ignorant opinion - disingenuous.. As anyone who collects swarms will know.
Of course the above is my opinion and there are many people who sincerely believe local is best - and in their case it may very well be true. But to extend that logic to the entire countrywide bee population is just unscientific.