I have been a long time user of Canon M's, starting with the original M in 2013. I got the kit with the 15-55mm lens. It seemed very well made and had fairly good image results. I added the 22, then the 11-22, which wasn't sold in the US at the time. Then I got the M3, which was an improvement for me as it had the EVF. I then added the 55-200 and the 28mm macro lens. When the M5 came out I got that. The 15-45 lens came along as it was the best way to get the camera early at the time. I then got the Rokinon 12mm lens. I also had a couple of adapter so used my collection of EF lenses from my 5D mk II as well. As the M3 was compared poorly with the M5 I rarely used it so decided to have it converted to IR by LifePixel. I was sold on mirrorless and preferred the M to my 5D for much of my shooting. I was fairly committed lens and camera wise to the M system. I felt unhappy with it, however, as my most used lens was the 24-105 L lens on my 5D. I waited patiently for Canon to come out with something equivalent for the M. It made so much sense to me that they would given how popular the 24-105 was in the EF world. I didn't expect an L, just a high quality lens faster than f5.6-6.3 with a similar focal length range. Fuji had one for their system, Sony had one, surely Canon would follow.
So I waited, and waited and waited. I liked the small size of the M system but didn't have the lenses I wanted although I had most that were available. In addition, my 55-200 seemed to always deliver sub-par image quality for me. Some (including Dustin Abbott) said their 55-200 delivered excellent IQ. Not mine. Copy variance everyone said. I hadn't encountered this in any significant way in the FD world that I started in or in the EF world.
Then the R came out. Mirrorless with full frame, like my 5D. It had been long awaited. I got one, with the RF 24-105 L lens, on sale shortly after it was released and quickly sold my 5D and EF 24-105 lens. I was now using the M and R cameras. In the fall of this year I made a trip to Turkey. I needed to decide what camera to use primarily. The R fairly easily won out even though it would be bigger and heavier. The M5 would come along as backup and with the 55-200 for telephoto images as my only EF telephoto at the time was the 100-400 L v ii, which was way too big and heavy to take on this trip. I took the R with the 24-105 and the EF 16-35 f4L, as I would be shooting inside mosques and other buildings.
When I reviewed my photos on my return from the trip I was very happy with the color and sharpness of my photos with the R. The photos from the M with the 55-200mm were disappointing and regretted having relied on what I knew was a sub-par lens. I immediately went on ebay and found and essentially new EF 70-300 mm L lens for less than $700. I had considered buying this lens before the Turkey trip but didn't find one at a price I was willing to pay. The idea was to use it with the M5 instead of the 55-200.
Now to the present. There were extremely attractive prices recently on the RP. In looking closer at the RP it was about 2 ounces heavier than my M5 and only slightly larger, but FF. If I was going to use my 70-300 on the M5, why not use it with an RP? Add t this my disappointment that when the M6 mk ii came out there was no M5 Mk ii. I strongly dislike using the back screen for shooting and much prefer an OVF orEVF. The RP had this too, so was close to the M5 mk ii I wanted. I had waited for the 24-105 M equivalent and was now pretty certain that one wasn't coming. There didn't seem to be much of a prospect for the M5 mk ii either.
So I got the RP a few days ago. I love the way it fits my hand. Much better than the M5, which I actually did like and equal to the R. Most of its increased size comes from the larger grip, which makes it such a joy to hold. I used it today to photograph family Christmas morning activities with the 35mm f1.8 STM that I had bought for the R. It worked beautifully withe the eye tracking enabled. The photos are great. It was light and very easy to use.
Everyone, including myself, talks about the M system being great for travel due to its small size. I agree, except my primary travel lens is the 24-105, which is missing from the M system. The 11-22 is great for wide angle shots, but I do more shooting in the 24-105 range in my trips than in the 11-22 range. I read repeatedly that one should select their camera system based on the lenses. I agree with this. It is how I got into Canon with my the FTbn in the mid-70's. Canon's lenses at the time were as good,, or better, than Nikon's, and often cheaper. Now this is leading me to the R as my primary system. I will keep the M5, for when I need to get the longest reach possible with my 100-400 and 400mm DO lenses, and continue to use the M3 for infrared. It is very unlikely I will buy any further M cameras or lenses and will sell, if possible, some of the ones I already have. I will probably end up with just the 11-22mm and 18-55 for the M3 for IR.
I am glad to have used the M extensively when it was the only Canon mirrorless option. In retrospect, hindsight being 20-20, I should probably have moved to the Fuji system early on and not expected Canon to bring out more advanced lenses for the M. But I was heavily invested in Canon and that seemed too big a leap at the time. But I am looking forward to enjoying the R system for the foreseeable future.
Mark