To fairly evaluate the value of these things, the company would need to provide you with additional data. E.g. if this were a public company you'd want to know

To fairly evaluate the value of these things, the company would need to provide you with additional data. E.g. if this were a public company you'd want to know the total number of these units, and how profit would be split between these units and other things (dividends, reinvesting profit in the business, options for senior executives, etc). You'd also want to look over the financials of the company from a few annual reports to get a feel for if this company was likely to even have any profit. Since this is a young startup and they are not willing to disclose information that would let you estimate fair value of these units, regard them as having zero value. Make sure you get paid in enough cash + bonuses with contractually agreed conditions (Non discretionary) + benefits for the total comp to be competitive with other options available to you. you could suggest in negotiations that the profit sharing units allocated to you vest over a number of years so they could serve as a tool for retaining your services and aligning your interests with the business in the long term, but not as a factor in evaluating your compensation package. (you don't have to point out it will be an ineffective tool if there is no profit/the units are constructed to be otherwise worthless)