I like kits in theory, but in practice I find it to be just annoying and not worth the trouble. I would go for an assembled SMD board, possibly letting the end user solder on through hole connectors or similar, then mounting it in the case.
I have two basic problems with kits as a user (as opposed to a seller). The first problem is that even though I consider myself reasonably competent, I find it fairly difficult to assemble a board designed by someone else. It takes me a lot longer and I make a lot more mistakes than if I had designed the circuit and PCB myself.
The second problem is that there isn't much value added by the kit. A nice thing about DIY is that you can modify/tweak things to your liking, but by the time you get a pre-made PCB and a box of parts, there isn't a huge amount you can do. If I want to modify the circuit in some way, I probably have to respin the PCB anyway. Maybe I could drop in some gold plated parts or tweak the sense resistors to change the range , but if the design is well optimized it is going to be hard to dramatically improve the performance or capability without changing everything around anyway.
So while I like the idea of a kit, I think it is more trouble than it is worth for both you and the customers.