The one at Victor's Kitchen cannot be categorised as 流沙包. Is just a normal custard bun.
Recently we tried the one at Bosses, 黑社会. Was very flowy. So flowy that if you are not careful enough, the filling will leak. I find that the salted egg yolk taste was too heavy though. Not ideal. Bean had a few bites and she loves it. Hehe
P/S: Still can't forget the ones we had in HK. *slurp slurp*