I'm using 3HK $78 (no admin fee) 4G 21Mbps 5GB (用完就停). Its reception is quite good (my usage is 99% at HK island). Regarding "轉台", I think it's a bit difficult to look for similar $78 5GB plan (no admin fee!).
Causeway bay
3HK 21Mbps -> DL / UL : 23.0 / 23.2 Mbps (收爆)
Birdie free sim -> DL / UL : 14.1 / 15.4 Mbps
ps.
birdie is also ok, however, I don't think they would offer 21Mbps 5GB plan at $78 or even lower (and no admin fee)