these "better 4 prong bars" might be great, or might do what many crash bungs do - many aftermarket crash bungs write off bikes in minor crashes - tearing the frame at the mounting point
the frame on a GS1300 is a cast thing (of not very high quality material) with a wall thickness I would hope was all calculated by experts in CAD - thus BMW should have a thickness on the frame rail / wall that gives just the frame rigidity required for their nimble handling and nicely supports the engine power with very little wriggle room - otherwise they would be wasting money on each bike and adding weight they didn't want...
so the frame rail where touratech land the forth prong was never in BMW land ever expected to take a side loading in any form - the very fact BMW do three prong engine bars and do not have a forth waiting to punch a hole in the frame - might be an oversight - or might be very intentional - indeed there are multiple you-tuber video's where hoddies are throwing bog standard BMW enduro spec bikes on the floor deliberately - and I never saw one say the bars bent or were useless (noting, of course we can have different levels of arguing with physics)
now touratech might have done vast research and landed on a spot of great strength and spread the load very carefully - landing a much better solution - but I think more likely, they are big headed, over priced jokers, who never thought about the consequences