Sticking with my motorsports analogies for a while...do you want to buy a "kit car" or a Ferrari even if the Ferrari costs more?
I am a big fan of Top Gear and watch most every episode at least once. From time to time they will air an episode that features some sort of "kit" or one-off vehicle from a small manufacturer or garage. Often times these vehicles have breathtaking performance and attractive costs when compared to a Ferrari. But they usually end the broadcast with the conclusion that, great as the "kit" car might be, they would not buy one.
Time after time these "one-off" vehicles break during Top Gear's testing. When that happens the crew has to wait for unique parts to be delivered or sort out the problem without the benefit of an owner's manual or factory service department to call. Even in cases where the vehicle performs well they find that it cannot be licensed for the street or has no DMV certifications. So they conclude that a buyer would be better off to spend a bit more and purchase a vehicle that is tested, certified, and supported by a company that is large enough to stand behind their products for the long haul. Both solutions can provide exhilarating transportation but only one can be counted on to provide that transportation for as long as the owner keeps it.
The same question should be asked regarding HVAC equipment. There are many small businesses that can purchase components, sub-contract the sheet metal, and hire temporary help to assemble units. But the end user is basically getting the HVAC version of a "kit car". The first cost might be attractive but certifications, IOMs, application and testing expertise, technical support, and supplier financial strength will all typically be important missing ingredients.
For some speculative buildings the "kit car" solution might be chosen because the developer knows he will soon pass the potential problems off to the new owner. But for larger corporate owners and developer/owners is the "kit car" solution really the right answer? Those end-users are investing in a building that will last years...they deserve an HVAC solution that matches that time frame from a company that will also be around to provide support for the duration.