Firstly, sorry to hear about your friends issues with the diagnosis thus far…..
So, to the crux - firstly, are you sure the diagnosis is Type 1, as opposed to Type 2 Diabetes? I only ask as whilst Metformin (Glucophage as a trade name/branded item) can be used, it would be highly likely if not an absolute, that he/she would also be on some form of insulin treatment if a genuine Type 1 Diabetic. This would make a difference, especially I would think in the early days - as if using both insulin, Metformin - quite likely to end up with a “hypo” situation as you come to terms in using both insulin and Metformin, this may explain your friend’s rapid blood sugar low?.
As to the difference in Metformin, my understanding is in the main two versions exist to try and limit gastrointestinal discomfort in the non-slow release users, by using a slower release version (SR) to essentially not “hit the body like a sledge hammer” (I.e. - you won’t **** through the eye of a needle for weeks on end if using the SR meds). There are equally base Metformin levels beyond my knowledge and I’m sure someone will correct me if my interpretation is in error.
You mention the “tense” situation with your friends AME and GP - can I ask as to what and why? If they feel they are not being treated fairly, then if like in the U.K., then you can always ask for another doctor diagnosis and opinion, or better still seek out a good endocrinologist, as they are the experts here - and at an AME and GP level, Diabetes can be very badly understood in my experience, and in the past (luckily now I have a brilliant AME) my diagnosis was missed initially by both parties - my old AME at the time was more interested in referrals to colleagues - and he did like to come out with phrases such as “oh, you need to go and see my good friend….” - be careful, as this quite often involves having your wallet “raided”, and for what benefit to the referral AME - who knows?.
In summary, be careful. Again, If like in the U.K., and you genuinely still feel aggrieved - refer to a professional body such as the GMC (or similar) for advice and recourse, as all practitioners are likely required to register and be licensed. You can also search out the practitioner by name here in the U.K. and see details on the person, to check credentials and alike.
Link attached to try and explain the Metformin query;
https://www.rxlist.com/glucophage-drug.htm