You may install "Booxstor firmware" to any
M92 device (it must be hardware identical, in Russia are sold also hardware modifications without audio output and also without pen ability, I guess) unless
it is ArtaTech one.
I did not buy from Booxstor shop, but I may install this firmware. And Booxstor gives me support, helps to implement my ideas and fix the bugs.
The price difference is not 70 EUR, but cca 30-40 EUR, if I consider missing cover and power adapter, and cca 0-10 EUR if you also consider the difference in warranty.
But if you want to "save" money do it. You asked for answers, you got them. What you do is your decision.
To be fair to Arta Tech, you get better TTS, and some cloud capabilities, if you buy their device. So, the price difference is bigger than stated in my previous paragraphs. One must count for TTS, at least.