Does the compact seem hard to conceal? I am in a toss up on the XDM40 or the XD40sc.
Very hard, yes. Wait, you mean difficult,lol. (j/k)
Yes and no. I would not want to slow dance wearing it... I am 6'2" and 180lbs with no *** so many full/mid size guns present a challenge as far as concealment. However, I live in an area of the country that a sweatshirt or light jacket is comfortable for all the summer months except about 2 weeks in August. The style of clothing I typically wear makes a big difference as well. I tend to wear slightly baggy, un-tucked button down shirts which work great for me, as far as concealment.
Today is a special day at work and I
really dressed up (lol) with a tucked in, long sleeve T and if you were not looking for it, I don't think you would be able to tell I was carrying the XD- other than, when bending over where the pistol clearly prints. Personally I think 90% of the population would not even take notice (other than other permit holders who would recognize a pistol "printing") I am fortunate to live in a very gun friendly state though so my point of view is based on this reality. It may be different if I lived in one of those
other states.
I would buy the XDM40 hands down over the XD subcompact but if you are looking
specifically for a concealment piece the subcompact would probably be a better option. I would probably not choose either as a primary CC.

I am currently having a love affair with this gun though so it accompanies me everywhere. It's a great shooter, it's winter and I can manipulate it well with gloves on, I have had exactly zero malfunctions in the 400+ rounds I've put through it with several different types of ammo, and with the compact coming with the full size mag with grip extension it was an easy $500 decision. When the XDM 45 comes out, I will be drooling at the door.