I think in some ICOs, they give participants big bonuses because there is no any other feature which attracts investors. Such ICOs with big bonuses fail.
For those ICO offering bonuses is not a bad idea at all. This a marketing strategy to attract more investors in their ICO project. Maybe an investors should make some research before investing their hard earned money.
Too many pre-ICP/ICO projects now. This is a lot of work for reading whitepaper.
Many of them hide the hash algorithm & volume in the post. They are wasting your time that they even don't want you to know any technical indicators of coins.
You can read some good reviews to make a short list of interesting projects and after that read only a couple of whitepapers. Anyway, you should read whitepapers if you want to buy it. And regarding bonuses, it's a good strategy for the company also because it helps to make a good ecosystem and strong community of people who support the project and believe it will be successful.