The minimum amount buy back seems reasonable, Hive-Engine when it comes to small amounts is pretty easy to use. One concern I would have is that I feel there should be a ceiling on the buy back also. When LBI are purchased even a small amount of investigation would show it is a Long term token.

By having the open buy back there is a risk of people using that function as a means of making LBI a short term investment. Any artificial decrease in the amount of investment power I feel would be a detriment to the earnings potential.

It works for SPI, because like you said SPI is a liquid pool with off chain assets.