It's been awhile since I posted.
I have had the Surface Pro 4 for over a couple of years now and at first when I got it I almost returned it within the first couple of weeks. I put it aside for awhile and about a month later started to actually use Softplan on it. I completed two projects on it without using another computer and forced myself to use it exclusively for only those two projects. Both were about 4300 SF and had fairly complex roofs.
I used it as a tablet in my lap most of the time without a mouse or the keyboard attached using only the pen and the onscreen keyboard.
I thought I could use the pen totally in place of a mouse and it was extremely cumbersome. The biggest problems were not having a left or right click option so I had to use the escape key to end most commands. The wireless mouse I ordered did not have a middle wheel so trying to rotate a 3D model was impossible. I replaced the blue tooth mouse with another that had the wheel so I ended up using a mouse anyway.
I don't use the Surface Pro for Softplan anymore but what I do use it for is online client meetings. The ability to hand sketch is a huge help. Instead of making changes and client "what ifs" in softplan itself I make a screen clip, move it to one note and quickly sketch over it as clients see the different possibilities. Very quick and when the meeting is finished I go back to softplan and make the changes.