I have both the iCarsoft (albeit v2) and the Carly. I had the Carly for over 10 years now (upgrading the software and the Dongle over the years), and the iCarsopft for 5 years (had an Autel before I had the iCarsoft).
I think you need both...
or at least I got both because I couldn't make up my mind.
The Carly is the more advanced tool, very very easy to use, and it generates PDF reports that can be stored in an online library. Plus, for a bit more you can unlock it to cover additional marques.
The iCarsoft is an old-fashioned handheld scanner, with an ancient user interface. And, unless you buy the CR version upfront, you won't be able to add more marques after purchase. BUT it is more accurate, can read more live data, and in my experience it was able to erase faults that Carly couldn't.
I no longer have the Merc, but while I did, for regular scanning, I used Carly. When dealing with a particular fault, I used the iCarsoft.
If I had to choose only one... it would probably be the iCarsoft. It's simply the more-serious tool, even if it is not as great-to-use as the Carly.
Hope this helps.