You can see that these guides all pertain to x86 devices and thus have a lot in common.
x86 (both modern and ancient) is a great platform for running OpenWrt, but it requires some work, since there is a wide variety of hardware that can be present on an x86 unit, and OpenWrt, being first and foremost a compact system, needs some human help in figuring out what it has at its disposal and how to use it...
Keep in mind, however, that x86 also tends to be more power-hungry compared to, say, ARM.
Also keep in mind that similarly looking devices sometimes have radically different innards. For example, one of the guides referenced above is about a Sophos device. Sophos has several product lines. The XG and SG devices are x86-based, so OpenWrt can be installed and configured without a hitch. The RED line, meanwhile, is built on Freescale CPUs, which is not a supported OpenWrt platform (not yet anyway).
If you're curious about a specific device, ask (but please try Googling first; it's entirely possible that Google has heard about interests similar to yours already).
This is not necessarily true, a well selected x86_64 device will draw somewhere between 5 and 12 watts - modern high-end ARMv7/ ARMv8 based wireless routers easily need twice that much (not all!). Admittedly, the need to run a dedicated AP (and maybe a switch) in addition to the router itself might push the aggregate power requirements beyond that of a single all-in-one device, but many users with advanced requirements (more than 4+1 ethernet ports or multiple APs to cover the whole house) will need those anyways.
My slightly dated baytrail-d based gateprotect GP-7543 needs 11 watts.
The MX60 passed its end of support in October, so companies that had those units are purging them left and right, and they are available very inexpensively. And, believe it or not, there's a guide for that, too:
I agree, hence, the "tends to" in the post you're quoting. There's an untold number of old x86 devices out there though. I don't measure power consumption, but I do pay attention to power requirements as a rough indicator of peak power consumption (emphasis on peak and rough). I realize that peak and typical are related only loosely, but they are related nonetheless.
For example, the Cyberoam devices mentioned in this thread are rated for 12V / 5A, so peak power consumption is 60W. For comparison, most x86 Sophos devices require either 12V / 3A (36W) or 12V / 3.33A (40W). So yes, there is clearly a wide range within the x86 realm.
Outside the x86 realm, though, a 4+1+WiFi device is likely to require something like 12V / 2A (24W) or even 12V / 1.5A (18W). And yes, there are ARMv7 and ARMv8 devices whose power consumption is far above that. So once again, I agree.
Don't you need a device with a radio to be a WiFi client?
I'm going to go with you are looking for something without radios
A NanoPi R2S (get the machined metal case it comes with to keep the CPU temp down) ordered direct from Friendly Elec is, I think, what you may be looking for: inexpensive, very low power draw, well supported by OpenWrt, decent memory (1GB), uses an SD flash for the OS (so you aren't going to run out of space there), enough CPU (4 Arm A53 cores at 1.2 GHz) to be a VPN server (~300 Mbps Wireguard), CPU is capable of hardware encryption if OpenVPN is a possibility (OpenWrt support looks like it will arrive soon for hardware encryption).
Finally, if you need a client radio after all, you can plug a WiFi dongle into its USB port. I've not done the latter yet though, so I can't comment beyond Friendly Elec advertises that is an option.
At any rate, take a look at it and see what you think. I've been pretty impressed with the R2S when I test it out as my spare Gateway router.
Yes, you are correct, I do need radios to receive wifi. I guess my point was that I do not need to pay for radio that can emit good wifi. But maybe there is not really a significant difference in prices between a pc's radio and a router's radio.
because you can get a lot of fun doing that, money is a money, emotions are priceless) for ~400 usd you get a 10Gig businesses class hardware, no further upgrades, no reboots, no performance issues, just setup openwrt, press poweron button and forget
I would avoid a mini PC if you care about energy. Intel has gotten irresponsible with power consumption (not just 12th and 13th gen which are insanely power hungry) but their new N5000 series draw upwards of an absurd 20-30W.
Good choices remain: Intel J4105 based, it's dated but efficient, a lot of them come with a few i225v 2.5gbe ports and run $200 online. Or get something like a NanoPi R4S for $80, it's supported by OpenWrt, cheap, and is quite peformant in the 5-10W range.
Good link, the idle is certainly reasonable, I read the higher wattage under load on a review website which recommended just sticking with the J4105 unless you need the performance. I'll try to find a link.
Are you sure the thing you are asking for is the thing you want? You asked for a VPN server that is not a router or AP, and is a client off a wifi network, and runs SSH. That is a strange mix. VPN is for securely connecting networks over insecure connections, but WiFi is secure, as is SSH. That's 3 layers of encryption... for what purpose?
Regarding your questions:
It's easiest to install and maintain on a router that is popular with the OpenWRT community. You get all the needed drivers, and you benefit greatly from other people testing/tuning/fixing a broad range of functions.
A router is a small computer that is purpose built for it's role, and enjoys significant economies of scale. Other small computers cost more because they include hardware that routers don't need (graphics, audio, robust storage) or don't have the same scale.