I am more interested in how well both systems work out in the field, and the kind of issues real life macro photographers face when they are out there!
All Nikon R1/SP90 images and measurements/info are courtesy of JW. You can also check out his thoughts on the R1 in that link!
Front view of the Mounting brackets. Note that the bottom part of the bracket for the MT-24EX (left) is trimmed off/flat but that's not the case in R1C1's mounting bracket (right).
MT-24EX mounting bracket's diamter is 9.5cm but it's trimmed by 1 cm at the bottom. The R1 mounting bracket's diameter is 11.7cm, no trimming!
Rear view of the Mounting brackets.
Mounted onto my MP-E65 macro lens on the left, and R1 onto Tamron SP90 on the right.
It is very obvious how much bigger the R1 bracket is!
This is how much the R1 bracket protrudes beyond the lens barrel:
Again, you can see clearly here that the MT-24EX mounting bracket is trimmed at the bottom and that the bracket doesn't extend beyond (radially) the MP-E65's lens barrel, and therefore allows me to shoot from really low angle, as low as the lens would go on a flat surface! On the R1/SP90 combo, however, the bracket protrudes out (radially) far beyond the lens barrel. Needless to say, the bracket will get in the way and prevent you from getting really low when you try to photography something on a flat surface.
I made some rough measurements in CS5. It was about 21 degrees on the MT-24EX/MP-E65 and 33 degrees on the R1/SP90.
Besides the bigger diameter of R1 mounting bracket, the thickness is an issue as well. The MT-24EX mounting bracket, once attached to the MP-E65, is about 12mm (see the image below) ahead of the front element. The R1 bracket will extends out quite a bit. You can tell from the image on the right above the "depth" (the distance from the front of the bracket to the front of the lens) was really big!
The corresponding measurement for the R1/SP90 is 35mm.
The corresponding measurement for the R1 is 2.5 cm (horizontal), and 9.5cm (vertical)!
Therefore, the SR200s are not only higher but also extends out quite a lot from the front of the lens. This tends to cause shadow on the lower part of macro subjects, and also very small/thin and dim catchlight as mentioned in this post and this post.
This image was taken by JW using his SP90/R1 macro rig. Not the very small/thin catch light in the spider's eyes. With the concave diffuser he is using, bigger catch light is to be expected unless the light angle is too high.
The catch light should be bigger, like this, when using the concave diffuser.
Photographing an arthropod (or any other macro subject) at its eye level or even lower gives a very nice perspective as opposed to photographing it from a higher angle!
Others: The R1/R1C1 is wireless though. But the MT-24EX can be configured to have the focusing light turned on by double tapping the shutter button. On the R1(SB-E200), however, you can only turn on the focusing light by manually pressing the button on the each of the two R1(SB-R200), or once, on the SU800 (for R1C1).
Okay, so you can put like eight R1 (SB-R200) on the mounting bracket and make a beauty dish out of it for fashion model shoot, but what's the point of that when it can't do the very job it's designed for properly?
Anyway, the main issue here is the over-sized R1 mounting bracket, but it shouldn't be too difficult to DIY a bracket to hold the two SB-R200 better. You can look here for ideas.