Mine is a physical ECU tune. Took about 8hrs to amend the relevant lines of code & still a couple of hours to fine tune the remap applied a few weeks ago. I'd not touch a tuning box or piggy back tune with a barge pole on an F10 M5. Fine for a 320d but not an £80k motor.
I don't understand your position on piggybacks--have you had a bad experience or did other evidence lead you to conclude this?
This is my second F10 M5 and my fourth F10 since their launch; the other two F10s being 550Xis. I had Dinan Stage 3 on the first of the 550s and was happy... until someone told me about the BMS JB4 piggyback. So I bought one and stacked it on top of my Dinan Stage 3 and added a little less overboost than the BMS-norm--the car felt different in a very positive way and the numbers backed that (I'm afraid I forget the specifics, it's a while back).
When I sold my first F10 550 and got another new one, I simply pulled the piggyback-box out of the first 550 and installed in the second one--job done. I cranked up the boost this time knowing that I was now running stock-boost due to the lack of Dinan and ran the car for a few days. The new car with the BMS piggyback alone was significantly quicker than the Dinan only mod and exactly the same as the stacked Dinan + reduced BMS--so what was the $5,000 for that I'd spent on a Dinan ECU tune and an exhaust (there was certainly not $1,000s worth of exhaust note in there or drivability gains--they drove the same--and as for the warranty, I can take the piggyback out in about 10mins should that ever prove necessary but my dealerships don't care, perhaps others do, though).
Finally, I decided I wanted yet more power and got an F10 M5. Again, I took the very same BMS-piggyback box out of my 2nd 550, configured its firmware via my laptop changing the setting named "Future Use D" to 1" per Terry's (the "B" in BMS) instructions and set the boost to +3.5psi. I followed folks' guidance on the forums and performed a few 40-80mph 3rd+ gear runs numerous time a day and let it adapt. Finally, I took the M5s for a few independent dyno runs and they've consistently put down 620rwhp on pump 92octane gas.
So, in short, I don't do Dinan anymore.
To date, I've bought just ONE box from BurgerTuning and it's moved from car to car to car with me performing perfectly every time in every vehicle with no additional out-of-pocket expense beyond the original box and new cabling when I moved to an M5 (total BMS cost to date across all three cars = $500).
My first-hand and 5+ years experience with Dinan, with BMS, with four F10s and well-over 200,000 miles leads me to conclude that, at least in this particular car and comparison, there's just no reason to spend the money on an ECU tune when the piggybacks yield better gains and to my first-hand experience, offer the same levels of reliability.