When it comes to the quad itself there are no difference. The only difference comes from the transmitters. The entry level 501s comes with the H901A FPV2Transmitter and the advanced version comes with the H906A FPV1Transmitter. Between these two quads the most notable difference is the range. The advance version gating up to 1.6km and the entry level at 800m max.
HubsanUS Support answered on February 14, 2017