The verdict

CPU
GMKtec NucBox T9 Plus has 1.4x the CPU throughput (6,200 vs 4,300 PassMark).
Plex
GMKtec NucBox T9 Plus transcodes more 4K HDR streams (~5 vs ~4).
Idle power
GMKtec NucBox T9 Plus idles lower (7W vs 8W) - cheaper to run 24/7.
Networking
Topton N5105 4-LAN has more NICs (4 vs 2) - better for a firewall or VLAN trunk.

Which wins for each job

Job GMKtec NucBox T9 Plus Topton N5105 4-LAN
Plex / Jellyfin ~5 streams win ~4 streams
Frigate NVR ~4 cameras ~4 cameras
Proxmox / VMs 6,200 PassMark win 4,300 PassMark
Firewall / router 2 NICs 4 NICs win
Local AI / LLM no slot no slot

Approximate - capacity estimates from curated specs, the same logic as the recommender. Verify against your exact setup. Prices move; check the retailer.

Full specs

Spec GMKtec NucBox T9 Plus Topton N5105 4-LAN
Price (list) $199 $189
CPU Intel N150 Intel Celeron N5105
Cores / threads 4 4
PassMark 6,200 4,300
iGPU UHD UHD
NICs 2 4
NIC model Intel I226-V Intel I225-V
RAM max (GB) 32 32
M.2 free 1 1
PCIe slot none none
Idle (W) 7 8
TDP (W) 6 10