In my personal opinion, if the end user wants to have a hardened device that's focused on mobile os security and privacy; taking a risk by adding an extra vector of varies variables/possibilities seems like regression. Which I might add, one would be paying an extra premium for on top of it all.
Our web method for installing GrapheneOS is straight forward and quite fast. May I suggest, if and when time permits, to take a read through our installation guide and get familiar with it. Specifically, making sure to have met all the required prerequisites is key.
This way, the user only pays for the device and maybe a peace of mind, of sorts, assuring oneself of unnecessary uncertainties have been mitigated appropriately from the start.
When it comes time to do the installation, we have a live chat support on our matrix community space in case any questions pre/during/post install should arise.
Perhaps then, if the end users feel satisfied and would like to contribute back, we have a number of options available for donating to help support the developers and project. Rather than paying some third-party (that would end up using our web installer anyways and charging you extra for it, etc).