When you purchase an alarm system from a company you are essentially buying a service not a product.
The companies will support specific control panels for many reasons, they maybe knowledgable and trained with that manufacturer, have stock available at short notice the panel generally fits the companies operations in well established places.
Asking someone to install a system they can't support or have no knowledge of is a bad idea, you will likely get a poorly installed system with at least teething problems.
You honestly need to decide which route to take, are you DIYing or are you having it installed. If the latter then of your quotes go with the company you feel most comfortable with, forget about the brand (just make sure it's 2 way if wireless).