I recently bought some Unifi hardware from the newer AC range, installing LEDE is becoming more of a mission. We use these a lot for custom hotspot gateways.
These are currently flashed using the mtd command or through uboot and a USB serial cable, however it seems that Ubiquiti have removed mtd from their newer unifi firmware so you need to first downgrade before being able to load LEDE - however its only a matter of time before the older firmware is no longer available and Ubiquiti starts blocking downgrades in newer firmware - so there goes that method of flashing.
Its also widely known TFTP can't be used (holding in reset while powering up to access recovery mode) because firmware images are being signed, anything not ubiquiti is rejected.
Which leaves the uboot and USB serial cable or JTAG as the remaining methods - both of which require opening up the unit which Ubiquiti have also made very difficult on newer designs, you almost need to break the casing to get in.
Does anyone know if there's any other easy method apart from mtd to flash these?
i've recently came up with an idea how to flash locked/signed firmware on litebeam ac gen2. basically you start flashing same ubiquiti fw that is already on device and interrupt the process, that leaves mtd partitions unlocked and you can flash another image to these using dd. more info in this GH comment-> https://github.com/openwrt/openwrt/pull/689#issuecomment-493658317
Another way you can do this, (which ubiquiti will have no way to block) is to re-flow the spi-flash chip with hot air, remove it from the PCB and then program it manually via SPI reader/writer. I think most are in the 8-SOIC package so are still fairly easy to remove with tweezers and hot air. SPI programmers can be had on aliexpress for a few dollars. Re-flowing the flash chip back onto the PCB can be done with solder paste quite easily, it doesn't matter too much if the chip doesn't line up, as when the solder paste melts it pulls the chip back into place on the pads.
Also while you're at it, might as well replace their horrible version of u-boot with an open source one.