Tax strategy involving investing in a start up note + personal guarantee. Am I missing something?

Hey all, got a question for those of you who know tax planning or business structures.

My CPA pitched me this strategy where invest thru a business entity into a vetted start-up company who is already functional and developed. Here is an example of how it would work - Invest $100k into the company and in return, they issue a $600k note to my business (Basically me buying their software), which lets me take around $700k in depreciation/write-offs in the first year. Huge tax benefits. Sounds great right?

I’d have to personally guarantee the $600k note. Which is not recorded anywhere and he assures me it is done in order to qualify for the strategy. However this part does raise red flags for me.

I asked what would happen if the company ever decided to call that note and ask for the money. The CPA told me not to worry, because they wouldn’t go after it, and even if they tried, they “wouldn’t be able to collect” since they won’t have the original signed personal guarantee.

The idea is that they will sell the company but for no less then to repay the notes and 150% of the initial investment. Therefore I will actually make money and they are firm in saying that they will not sell less than that..

Like, I’m no attorney, but I don’t want to be personally responsible for $600k over some loophole that could fall apart in court.

Is this kind of setup normal? Anyone seen something like this in practice? I’m not against taking calculated risks, but this feels like I could get burned if things go south.

Would love some real-world input before I move forward with this.