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This post is not financial advice. This post contains my opinions yours may be different and that's ok.
It's been a little over a week since the sustainable pixydust/hsbidao bot launched. This is the second bit the UNICOIN 
I had wanted a tipping bot for a while. I did see one major flaw in most tipping bots (not all ) and that is they are based on tokens held/staked and the tokens themselves are not backed by HIVE/ Hive-engine assets (at least further down the road). The result: price instability, inflation and lack of new funds coming into the token owner's account after pre sales/initial sales..
There is also a factor to consider when setting a bot up for tokens held or staked and that's good when there is a pre-sale or when the token is new because most folks will be buying tokens from the token creator at first. This can and does back the tokens, an give some income to the token creator obviously. But in a decentralized market, that quickly changes.
Let's say you have a tip bot that is tokens held/staked based. After a while new folks coming in or people who are increasing their stake may not be buying tokens from the token creator. That means there is little to no income to the token creator to back/mint new tokens from sales. This can be and is a huge problem for many tip bots/tipping tokens.
That's why I based my bots on HP delegated as opposed to tokens held. Not only does it allow folks to use the bot without needing to purchase tokens but it also provides a steady income to the token creation accounts regardless of sales. Folks keep and control their HP and can remove the delegation at any time.
I also implement buybacks and burns on all my tokens which reduces the supply. Though there will be less burning of PIXYDUST tokens because the supply is much lower.
All my tokens are backed by HP/hive/hive-engine assets before mint and remain backed. Having the tip bot be HP delegation based makes this sustainable as the HP for curation backs new mints. New mints are also backed by other tokens, but I think you get the point.
Even after more than a year since the UNICOIN launch some people still kind of scratch their heads when they read/hear about my tip bot and why I do things differently. People also associate HP delegation to upvotes. I do not run an upvote service. The votes on these accounts are separate from the HP delegations though there is naturally some overlap.
So why aren't other projects doing this? Well the main reason, in my opinion, is because no one had done it before and getting the bots the "see" HP delegations was hard AF. The logic in the code was , well not intuitive. That code is now on github so anyone who wants to do this has access to that code for free.
Is this the solution for all tip bots/ projects? Of course not. Everyone does their own thing for their own reasons. This is one solution of many possible solutions. However, could it help projects that are struggling with too much inflation/price drops /instability and lack of account growth, sales etc? Likely, yes.