[slotloco]

Good honest review there CMOTD.
Don't you also loosen the motor pod?

FWIW - for others reading. The weight, track and height are pretty much the same as the CA40, CA45 and CA50 Alfas, - which are all a mm or so wider than the CA35 Alfa
I have all the Alfa models and the Opel (actually 4 liveries have been released so far not just one)  The Opel is wider and lower, so has naturally faster handling

The Mercedes runs lap times on my track almost identical to the Alfas, so they are good running mates.
Mine have been taken a few steps further - but not 50 quids worth - just grub screw front axle height setting, softer braid for wood racing, glued and trued N22 tyres, weight to stabilise; and the usual minor fettling to improve the function of factory components. - About 5 quid per car .............. and 20 quid of my time :) 
With about 9 grams total weight on pod and chassis, they match an unweighted Opel, and are really fun to drive. Like you, I find them about 3/10ths slower than a Slot.it Group C around my 65 foot track.
They do have less motor, - the 21K MX15, whereas the Group C and 65 -80 sports classics have the 23K MX16