These would be very powerful as the number of gems you get from tributes goes up with the more tributes you get I think they would be worth it to buy! Especially if you are active a lot and collect a lot of tributes per day a couple extra gems per hour adds up fast.
This pet would be kinda hilarious and I would love to see it happen. It would be interesting to see how long it would take to break even in gem value compared to just buying a typical gem bundle of an equal price.
I don’t mind as is the only purchases worth making really are the DK armor and campaign passes, having a paid pet that is worth having would be a fair way for them to make money instead of trying to sell stuff nobody is happy to buy.