You have to be very careful about this since T-Mobile frequently and intentionally re-brands their 3G HSDPA service as "4G." But they don't claim that it's LTE. And to be fair, their HSDPA service is very fast. It doesn't qualify as 4G but all the available LTE in the U.S. also doesn't qualify as 4G (minimum of 100 Mbit/s).
Actually, the ITU changed 4G standards in 2010 to include HSPA+. It is why AT&T claims "the largest 4G network" while having less LTE than Verizon, why Sprint claims WiMax as 4G, and, as you mentioned, is why T-Mobile has "4G" (HSPA+) and "4G LTE".
Again, everyone I know who is on the T-Mobile $30 plan has LTE -- and I had LTE when I used to be on the plan. I think it is possible that they may remove LTE from that plan, though they haven't yet, and (based on previous experience) T-Mobile will likely grandfather current $30 plan users so that they keep their LTE.
While I think that Harbor Mobile deal is the best deal in prepaid right now (if you can live with T-Mobile's network), whether you would chose it of the $30 T-Mobile plan depends on your data and talk usage.
