100% of investments I've been involved in (30+) over the past 6 years have never included these kind of terms. As Danny mentioned, using a "Tranche" approach to progress / investment is usually a clear indication that the investors don't trust the teams ability to execute.

Risk capital requires risk, and it seems like they're trying to mitigate it.

I would use their interest to approach other investors and get better terms. Obviously you're doing something interesting if they're interested, just take that momentum and find someone else who's going to be a real partner.