Hope you are well.
It's a good question. From my experience - review exchange is kind of obsolete nowadays specially for indie developers. I am mainly talking about android as I have tried on this platform. The fact is google now calculates every aspect of a game to set the ranking. For example -
1. No of downloads
2. No uninstalls
3. No of bootups
4. No of positive reviews (also they keep track of the reviewer)
5. How long a user keeps a game in his device
6. Good related keywords
So you can see - only relying on good reviews or good keywords can't bring in any success. Because you can't be sure that any review exchanger will keep the game in his device for several days and play the game several times. So eventually you can see the reviews are getting removed and your account will be in danger of being banned in the long run. Huge pain.
For iOS I have not tried a lot but as far i can guess the fact will be the same more or less after the recent algorithm update from apple. So personally i would suggest not to rely on review exchange rather find some other ways to get visibility.
I would also like to invite other members to come up with their own ideas and see what they think on this issue. Besides what could be the alternative way here?