last time i rented tools at autozone, i know there were some that fit on the inside of the coil. like you speak of.
that pic is of the harbor freight compressor, which are complete trash, not worth the metal they are made with.
on my tundra springs, which ive done twice, the spring rate is high and there is not alot of space in the coils to put the feet, but you can manage, even if you have to tap it in. there is no way that benz has stiffer springs than the front of a tundra...