The closest product to the IX2 would be a TS1200 (2 drive unit). At 4TB, the TS1200 is half the price on Amazon. The TS3400, a 4 drive unit that does support iSCSI, is about 2/3 the price of the Lenovo/Iomega 2 drive device for a 4TB unit. The most expensive 2 drive TeraStation available, the TS5200, is still $200 cheaper than the IX2 and it has a faster processor, 2 NIC ports as opposed to one, 8x the RAM and a bigger feature set.
Given the processor and RAM in the TS1400, the rebuild time you mention is not unreasonable.