I own an EX2 Ultra as well as a Gen2 mycloud.
Architecturally, the two are VERY similar, (software wise.) The outstanding differences are as follows:
Gen2 stores the system OS on the disk drive | EX2 Ultra stores it in an MTD flash partition so you can yank the disks out.
Gen2 does not support hardaware port multiplier on the SATA port, but the EX2 Ultra does. (not advertized, but some disk drive products include a port multiplier to do their thing, such as with hardware raid-0 M.2 to sata adapters. These adapters should work inside the EX2 ultra, but wont inside the Gen2.)
Gen2 is based on a Marvell Armada 375 SoC, EX2 Ultra is based on a Marvell Armada 380 (–81, --82, -85 or -88) series SoC.
Gen2 runs at ~1.6ghz tops, EX2 ultra runs at ~2.6ghz tops (Both are dual core.)
Gen2 has 512mb of ram, EX2 has 1gb.
Some of the features that WD enabled on the EX2 series and not on the Gen2 hardware:
iSCSI target hosting
Active Directory enrollment
Advanced network parameters (like MTU size and pals)
RAID manager that is actually useful
Installable application support
Pretty much ALL of them can be enabled on a Gen2, but it will void your warranty. (See also, the “Install apps!” thread, aka, the WDCrack thread. It turns on all the bells and whistles on a gen2 but iscsi needs additional prodding-- see my thread on the topic.)
As for your question about attaching a MyBook directly to a router with a USB port-- Yes, it will “Work”-- however, that consumer router is pretty weak kneed compared to a real NAS. Even the Gen1 mycloud outclasses it handily.
(For reference, the router you specified can be found on wikidevi, here:)
CPU1: MediaTek MT7621ST ( 880 MHz )
FLA1: 128 MiB ( Macronix MX30LF1G08AA-TI)
RAM1: 128 MiB ( Nanya NT5CB64M16FP-DH)
The Gen1 mycloud has twice the ram, and a faster processor. the Gen2 mycloud has 4 times as much ram, and an EX2 ultra has 8 times as much ram.
Why is this important? Samba uses a fair chunk of memory to do its thing, and a router also needs free memory to handle incoming and outgoing packet buffering. If you tried to seriously do any kind of duty other than extreme light duty on that router using the USB port, your network performance would tank, and tank hard because the router would be bogged down hard with IO contention and memory constraints.