My only issue with the powerline adapter is that it's a product for a specialized purpose that likely becomes obsolete and money out the window very fast. It's like paying a lot of money for an ethernet extension cord which likely will not be necessary/useless within a few years with the way wifi network gear is improving and decreasing in price.
For $310, you can get this set with 3 units which has power line built in. It can improve the performance if you pull an ethernet cable to each node, but it's not necessary.
https://www.amazon.ca/TP-Link-Deco-P.../dp/B081ZWJ6FX
The version without power line is $175 (still 3 units) and at worst you need to spend an extra $20 to give your desktop wifi.
https://www.amazon.ca/TP-Link-Deco-W...C3D9XAD4SCZVK8
NOTE: I don't think the powerline back haul aspect of the mesh system is actually necessary to extend signals. It just makes the system even more powerful/robust than without the powerline built in.
Not saying that power line is a bad idea, but if you ever change things to negate the need of the power line to the garage, there's a high likelihood it will collect dust (money out the door). For slightly bit more, ($200-300) you will have a system that will have overflow benefits to the stability and signal strength to the remainder of your home and future networking upgrades your system may need in the future may likely already be done just by having this system. Heck, even if you are thinking you just want a patch solution because you might move or something, you just bring the mesh system with you and still reap the benefits vs powerline adapter may become pointless at another location.
Actually, now that I have stumbled upon this, the Deco P9 looks like the perfect lazy option my parents' place. The built in powerline backhaul is perfect as a lazy option to address the lack of ethernet backhaul option at their place. I just don't have the time to sort things out, so that tiny bit of premium to do it lazy style is something I will consider.