I'll start by saying I used these shorts recovering from a twin pregnancy... so my experience is probably a little different from a normal pregnancy... I had pretty massive muscle separation, and gave birth via c-section.
I was initially a couple of cm into the large size range, but as I expected to loose quite a bit of weight quickly, decided to go with the medium size in the shorts.
When I initially tried the shorts on day 2, they were way too tight, took me about 45 mins to squeeeeze them on and they were just uncomfortable. With having to go to the bathroom often to change maternity pads, and midwives wanting to look at my scar several times a day - the shorts were not my friend at all, and I put them back in my bag.
On about day 5 or 6, still in hospital, and with an aching lower back and still quite a bit of pain around the c site, I tried these shorts again. This time they took about 15 mins to shimmy into, and fit quite well. They were definately supportive and I felt very held together wearing them. They assisted with the pain in both my back and the c site, and also made me look less 'still pregnant'.
I still found the need to go to the bathroom, and reveal my scar so frequently made the shorts really impractical to wear as I was spending a lot of time pulling them back up. I found it horrible when I was struggling with the shorts halfway up and one or both of my babies started crying!! I also didnt wear these overnight because with so little sleep, I didnt want to waste any of it, pulling my pants up and down.
Another problem with getting these on and off, was the fact I was still very swollen/ bloated around my stomach, and the naturally wanted to stop just below this bump on the way up and down - and this was right in line with my scar site, so was momentarily pretty damn uncomfortable during this first week.
Also, they seemed to have 2 layers of fabric and I found I had to reach into the shorts and pull up the inner fabric to position them correctly.
Moving forward to when I was home from the hospital, and the 1-2 week post birth period is when I found these the most useful. I sill found them a bit time consuming to put on/off when I just really wanted to take a quick pee, but the support they provided finally outweighed this. Because of twins, I was doing double the normal amount of bending to pick up/ put down, carry, change etc and my pram was twice as heavy to push, and I found the times I was not wearing the shorts, my back was really aching a lot more.
After 2 weeks post birth, I had lost 15kg, and the shorts were now a lot easier to get on and off, but I felt they no longer were providing enough compression to be doing any real help. They still helped hold my tummy in a bit, but no more than any normal support undies would. I don't know if I should have tried a smaller size in the shorts. The other thing I noticed as my stomach deflated, was they body length became too long, and I had to roll the down a bit under my bra strap (I am 162cm).
With regards to helping my muscle separation, I am really unsure as I have nothing to compare it to, but this had improved from about 6 finger widths to 3 over the course of 4 weeks, and is now pretty much stuck there.
The physio in hospital gave me some tubigrip to wear around my middle to help support my back and help with my muscle separation and I used this when the shorts were in the wash. To be honest this provided just as much support as the shorts, and is a lot cheaper. It has the added benefit of only covering the torso, so once it was in place, you could leave it there all day. However it did roll itself up or down a little bit sometimes, where the SRC shorts stayed very much in place.
I really liked these shorts for only a very small window of time, so given the price, I don't think I would purchase them again.