A really good read on the timeline of Schick's is
here. As I've learnt the later the models, as represented by the ascending alphabetical order - the milder the Schick. Thus, a G is moe aggressive than a L as an example.
The two that I have are different as the M is an adjustable razor. Therefore, the dial allows for the gap between the blade and the bar to be increased or decreased. As Andreas pointed out, can be test for nowt via the Lending Pool. A real good try. A flexible razor in so much you can taylor the shave to your preferences. A little more aggressive, or little less so etc.
The J1, is fixed. No adjustment. It is a mild shave experience. However, for me - efficient. Does a nice job. As
@Fergiebilly mentioned, both will accept a twin blade. These can add a whole new experience to the shave. I guess that is another story.
Personally, I have never used a PAL injector. I hear they are very nice.
@sc0tt is selling what looks to be a very nice razor
here. Looks like the price has been dropped too!
Richard