In fact i have two pairs of Raichle AF600, one older "racing" model with the thermoliner but no "velcro" strap (on the liner, not the 4 on the shell), and another more recent exactly like Suzuka Deeluxe model (4 straps on the shell plus the strap on the standard boot inside).
In both cases, i want to keep maximum flexion (notably for EC) while having more precision and responsiveness (in particular on the older racing shoes).
Hope this helps you for advice on which Booster strap i should go for...
Thanks
Silver ;-)