I want to say first, airdrop is free. The bull market will start in 2025, and most telegram mini games are currently running. Although few projects are paying off so far. OP As you say many projects are asked to do ton transactions. Yes, it is true that they ask for transaction in almost all free projects, but it is not mandatory. If you feel like it you will, and if you don't want to don't. I think no money should be spent on freebies. If you spend money on it, you get some more rewards.
Few projects that yield?
I think it also depends on how you do it, if you get the first rank then you will have a lot of advantages from the airdrop.
See how Notcoin's success as the first Tap2Earn telegram Mini App made the TON network even more hype.
At first, it was very underestimated, but when it made a big income, many similar games began to emerge that rewarded participants.
Now you may only focus on the Telegram Mini App, but you need to know that the airdrop is quite extensive and not just on the TON network.
There are more airdrops that you can work with, by paying for transactions or even by doing new network tests etc.
Whether an airdrop is legal or not will only be known when everything is done and of course help from the community is needed.
I have a community that provides quite valid information about the airdrop that will be done, so I know what to do.