AT&T att LTE hotspot dilemma situation

hi there,

i have a question about the ATT LTE hotspot， currently, from ATT, there are only two kind of hotspot choices,

AT&T Unite and sierra 754s

but, i am looking for a small form hotspot in my pocket, the above two seems still bigger than my expectation, so i did my research , i found one(sierra 763s) may work compatible with ATT LTE/4G network,

it is the same manufacture, but different model, this one is smaller, and battery last longer.

but, i found it is only sold in CANADA, so i plan to buy one and unlock it for ATT LTE/4G network, my question is , will it works with ATT LTE NETWORK in best result? wherever there is no LTE coverage, will it work well with HSPA+ (4G)network?