I instaled a middrive motor bafang 250w and a Hailong 17A battery for 750eur but I did it myself following youtube videos , It works great, did not have the money for a shop to do it.
I added an EBO system to my older catrike 3 years ago. They were great to deal with. I went with a hub drive and its a great system. Came with all the correct cables. Bought the battery rack from hostel shop. I went with hub mainly because i can still use the system if the chain brakes and get back to where I started and I did have it installed by a dealer.
You didn’t mention that hub drive setups maintain all 3 rings up front making for better non e assist riding. I currently ride a 559 and a 700 and so far I don’t need it but when I do the 559 will get a hub drive. The 700 is built for pure natural speed on its own!
It is certainly possible for you to fit a third party motor system from someone like Bafang/EBO etc, it just needs to be fitted professionally (which your team would be able to do) and a maximum of 250w for it to not void the warranty.
As someone that is good with a spanner and fitted an aftermarket motor kit to my trike , I’d say letting the trike shop do the job if nothing else, because they can make sure you have all the right parts needed to do the job , buying an aftermarket kit does not guarantee you will have everything you need to make a good job , you can end up fiddling around for ages getting it dialed in.
You are so right. As a shop we are still making improvements for install of our aftermarket kits. When putting on an approved kit that the manufacturer has designed to work with their trike, it makes it much easier to install.