This is a German fudge unfortunately as they keep chasing higher performance aeroplanes...
Mostly the Germans do aviation quite well - but in this specific aspect they are living in a strange fantasy world all of their own.
It's not only a German "thing"; at least Italy, the Netherlands and France spring to mind as having the same or similar MTOW requirements.
The root of the problem lies in an inept formulation of the legislation, which manufacturers have simply exploited right up to the boundaries. Many of the very dubious designs, if you like, are actually not only German, but also Czech or Italian (how do the fancy Tecnam RG models fare with respect to these requirements....?)
In the UK, where the same aircraft are flown lighter, we have less accidents than Germany, and very few where a BRS would have helped.
If you want to compare microlight accident statistics between Germany and the UK, you'd need to take into account the number of aircraft and the hours flown to get a valid comparison. German pilots "flee" to microlight flying due to the amount of restrictions on "normal" GA flying; restrictions which you to a large extent don't find in the UK (e.g. flying under LAA auspices, the liberal use of farm strips). I'm pretty sure that you won't find as many microlights in the UK as in Germany.
Off the top of my head, I can think of three accidents where the BRS saved a German microlight pilot's life: A RANS S6 (I think; it's on Youtube) colliding with the tow cable of a glider tug in France; an FK14 entering IMC near Cologne, and a weight-shift microlight which came apart in the air in Bavaria many years ago (I saw it happen).
In Germany, BRS is mandatory as a compensation for the relaxed certification requirements for microlights. I like it, feel comfortable knowing it's there, and if it saves a life, whether due to pilot or structural error, that's great!
As a concession, the MTOW was raised in Germany to 472.5 kg.
Hmm. Yes well I am a big chap. 1.92 and 94Kg. But I have a perfectly petite partner, so (once I'm qualified) our combined weight should leave enough for a toothbrush and a bit of fuel...
The problem will be finding a pocket-sized instructor to fly with while I'm getting licensed, I guess.
The reality is as follows: In 99.9% of all flights two-up in a German microlight, you'll be above the legal MTOW (structurally and aerodynamically you'll usually be OK; as far as the BRS is concerned I don't know). As long as you're not PIC, the blame will not be on you if something happens. Personally, when I'm PIC, I'll either fly alone or only take one of my children or a very petite passenger. I have no intentions of attempting to fight the insurance company afterwards, if something happens, even if exceeded legal MTOW had no bearing on whatever happened. In your case, it's your decision.
... and apparently all think that they weigh the same as Hanna Reich in her prime.
It's Hanna Rei
tsch, but this notwithstanding there's no need to use a historical person of more than dubious political convictions as reference - who nobody nowadays knows anyway - to get your message across...