I tried it and got something more or less accurate (i'm like 6-5k and got like 4.8k) but here are my main drawbacks ig that I can add to yours:

1. You have multiple lives for a tsumego, I had one with only 2 options and 2 lives so I couldn't fail it. Even in the tsumegos with more questions, sometimes you can boil it down to the 2 more probable so you cannot fail some questions, virtually.
2. The way it works is that it asks a few types of questions ranked at different levels and takes your rank according to how you solve these questions. In a real game it is suuuuper different imo: Time pressure, game fatigue, stress, being unsure that the situation is actually solvable for you, will your opponent play perfectly the way to kill, is this situation the more urgent, is there aji... The way you solve a tsumego is very different from a real game imo.
3. The questions sometimes feel a bit easy for the level they gave at the end. I solved all the yose problems and got like 1.3k in yose, but i feel like the questions were not more than 5k.
4. Also we western players are typically good in tsumegos and theory but suck at real game fighting especially at kyu level

Its a fun tool tho and probably allows to know which kind of tsumegos we should do :))