We have used the SWPro+ add-on for Apex some, it's usefull, but not as usefull as it could be.  It is very good if you drive the ditch track ahead of time and need to design a variable grade drain.  The best-fit option doesn't work well on the display, because it designs the drain using only cuts, and there are times that it is much more efficient to do a small amout of filling  along the path to avoid a long cut.  The Apex add-on would be much more usefull if it present a 3-D surface of elevation rather than delineating elevation by color alone.  It would also be nice if it highlighted where you were along the ditch-track path as you selected points on the elevation profile so that you could correlate high and low spots to a location in the field.

Where we were dealing with very shallow grades, and didn't have a feel for where the water needed to flow, we put the reciever on the four-wheeler and did a survey and then drove where we thought some of the ditches needed to go.  In that situation it was faster and more effiecient to drive it everything ahead of time and design the drains in Apex.  

Most of what we have been doing is correcting terraces, for the most part I think it is faster to just drive them with the tractor and scraper and design the drain in the field,  breaking the terrace into sections if variable grades are required. Its amazing how many terraces function (or didn't)  with significant reverse grades in them.

If you think you are going to put it on your Landoll grader I would advice ordering a counterbalance valve and an orfice check valve.  It will be nearly impossible for I-grade to control it without them.  We need the orfice-check in our Ashland scraper to make it run smooth.