I am going to defend MMR. I use it for every course I measure. I feel it is simple to use, and $30 per year is a small price to pay to get rid of the ads. Many of you spend much more on that for postage, envelopes, and paper to mail applications and certs to the next level.
That said, proper use of MMR allows for very useful measurements. I overcome the tediousness of trying to follow curbs exactly by allowing for some cutting of corners when I map. This is similar to our SCPF, in that my endpoints come out within about 20 feet of what I map.
I do have most race directors map their course first, then send me a link. I look at it, and normally have to tell them, again, they should have turned off "Follow Roads". It is easy for me to re-map it. A 5k may take 2 or 3 minutes to map, and a marathon can be mapped in 5 minutes, or less.
I can then export the route as a GPX file, and put that onto my Garmin Oregon. I follow it while measuring, which is much easier and faster than constantly checking a map. I don't know if the other programs allow you to export a useful file.
To me, MMR is a great tool. If used properly, it is accurate enough to plan a course very well. If it is not used properly, it results in a very inaccurate length of any course. Likely no different than any other mapping tool.
Keep in mind, also, that every mapping tool that uses satellite imagery will be inaccurate, due to "rubber-sheeting" of the imagery. Since the images are not exactly rectangular in each photo, sides/corners are distorted a bit to make imagery match. If you look closely, you can see this at the corner of many tiles. I got this from the satellite imagery company itself.
Mapping tools, like any other tool, are only as good as the user.