How do you successfully do a joint venture?

So I'm looking for a little advice here. Hopefully I'm in the right place.

I've got a SaaS based product idea (let's called it MyProduct) and an associate has another product (ProductB) that deals with metrics that would bolster MyProduct but potentially less appealing as a product in itself. I believe MyProduct to be a pretty solid idea, viable and something that would work in its own right as a business. The current plan is to combine these products to build a platform as they would provide more value to the end customer.

We're at the stage where we need to figure out the commercials. Who's getting what and the like. As I've had the idea for MyProduct for a while, I'm reluctant to give away the intellectual property rights. I really want MyProduct to be successful and have the option to push that in my own direction if I see fit. I see the combined platform as being useful but simply less scalable.

The current suggestion that doesn't make a lot of sense to me is:

• MyCompany in a joint venture with TheirCompany with a 50/50 split of MyProduct

• MyCompany as a 25% cut of ProductB

I appreciate that there's probably a load more information needed to give an informed reply but any advice anyone might have, would be greatly welcomed.