as i know this is mercury protocol

Qute curious about this also. Would really love to see anyone answering this query.

Sounds cool. But why should investors buy tokens on project site, if they can do this on exchanges? How to shield tokens price from speculations? There can be situation, when investors buy cheaper  tokens on website and in the next moment sell them on exchange with extra charge. 

Because they support the project on ico. But tokens can be much higher after the end of ico and when they are listed on stock exchanges.

The security of tokens dont depends nobody!

I somewhere read that  sometimes  happens that the company after the sale lowers the price and buys back its own tokens, is it true?

I don't know, but tokens and shares buybacks is normal practice for successful companies. Companies without any problems can show gratitude to their investors and increase own market cap.

As I understand companies understand the value of their tokens, buy them and then regulate their price in the market.

Please friend, dont put reports down here.

Week 18.12 - 24.12
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Retweets:
18.12
https://twitter.com/Datariuscrypto/status/939882053516124161
https://twitter.com/Datariuscrypto/status/939865477874102274
https://twitter.com/Datariuscrypto/status/939804930134675456
21.12
https://twitter.com/Datariuscrypto/status/940872318368264192
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22.12
https://twitter.com/Datariuscrypto/status/940915890249523200