AT&T's 4G network is, indeed, LTE. And if the OP purchased a "4G" hotspot from AT&T it is almost certainly an LTE hotspot. My 4G/LTE mobile hotspot from Verizon runs from 7-10 times faster than 3G. The AT&T hotspot should have similar performance. But the AT&T 4G/LTE network is currently tiny compared to Verizon's (which covers about 200 cities in the US) and it will be another year before the AT&T network is deployed across the nation.
Another major advantage from my standpoint is that my mobile hotspot can connect up to five devices simultaneously. Thus, I use it for the iPad, my phone, and my laptop simultaneously. And because I'm allotted five gigs of downloads per month (for $50 on contract) I don't usually have to worry about exceeding that ceiling and being charged additionally.
For me, the mobile hotspot is a tremendous convenience because I travel a lot and frequently find that "free wifi" in hotels is worth what I'm paying for it. On the other hand, if the OP is a light user of a cell network, does not travel to or live in an AT&T 4G/LTE coverage area, and has already purchased an iPad with 3G capabilities, the additional value of a mobile hotspot may not be worth the $50 per month it costs.