The Time Capsule is the best priced Time Machine network target on the market.
No third party is going to beat every aspect of the TC.
I could NOT recommend the latest TC unless they get a very substantial discount in the refurbished store. If you buy one second hand it might work and might not.. even brand new ones do not have a great QA record. Apple cannot replace it once they run the stock out.. will they give you your money back after 2week return period??
My first TC Gen5 dead in a week. Second one.. ie replacement worked but the wireless was poor. I got rid of it and went TCless for a while.. bought a third one second hand cheap to play with. Has worked perfectly.. upgraded the disk.. excellent. Got a dead one for repair.. terrible.. hard to work on.. wired like iPhone.. not like the old Gen4 TC which was heavy cables and near indestructible to DIYer. Has stupid firmware options (not to outside world but internally they have used too much iphone code).
3rd party routers.. hmmm.. could be good.. but will work like my Asus.. is pretty much plug in and works.. you simply set the Asus to use the disk for TM.. and even better it appears then on the network as Time Machine target you can select in any computer.
However I keep having issues around 8 week mark.. something goes wrong.. not even the same thing.. I have to wipe the disk and start over.. not good for family.
You can buy a small synology NAS.. extremely easy to turn on Time Machine functionality. Has been very reliable.. but it will cost you a 2012 Mac Mini.. (you don't need Mac OS server app additions now as Time Machine server is built into High Sierra).
Either can act as file server for the network.. The Synology is excellent and is easy to open and change disks. It is FAST.. and works for all clients.. PC or Mac. Absolutely brilliant and highly functional firmware.
Do the sums and work it out.
I have not finished testing the Asus.. (or Linksys which I also got and is supposed to support Time Machine).
But my guess is they are not sufficiently dedicated to Mac OS and sold to Apple market.. so will never match your TC.