I used a pair to provide Internet access at a Customer's construction site back in 2010. Cell phone hotspot wasn't a thing for me yet. We took a pair of WRT54Gs, configured one as a WiFi client, the other as a bog-standard router/AP, connected the LAN from the client to the WAN on the router/AP, pur a directional antenna onto the "client", and pointed it down the road toward a big business who offered free WiFi for Customers. We leeched off that until the real Internet service got installed. (It was a restaurant and we ate there at least once so we were Customers, right? >smile<)
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They don't often offer inexpensive, deliberately-hackable units like the WRT54GL, I think, because of support costs.
And by "support costs," I don't mean that it was expensive to hold users' hands while they installed custom firmware -- that's never been a service that has been provided.
Instead, I mean that there are people who start goofing with this stuff and run out of skill when hacking close-ish to the metal on this kind of hardware. They don't know how to get themselves out of a jam and unbrick their device.
So they find a way to lie their way into getting an RMA and get the device replaced under warranty, and that's expensive for companies to deal with.
(Those people fucking suck.)