Ubiquiti has a good reputation for quality overall. Asus and eero also have well-regarded mesh network devices (at least according to The Wirecutter).
Nowithstanding John Galt's understandable personal grudge with Synology, they have some decently regarded NAS - although the top pick this year is QNAP (again, according to The Wirecutter's reviews). I won't argue, as I've been a long-time QNAP user. But full transparency, that was a matter of luck, when the first time I went NAS hunting I found a readily available QNAP and Synology was out of stock where I was buying. Now I'm comfortable enough with that system that I likely wouldn't change unless I had an experience like Mr. Galt had with his Synology.
All that commentary aside, an external SSD is more than adequate for backups. The value of a NAS is in all teh other things it can do beyond just hosting a backup drive. File and media servers, redundancy and RAID data protection, multiple user accounts and disk quotas...but that only matters if those are features you need or want.
