On 2800 (HK Tracker) the liquidity is fine. If you want exposure to the HK index then just do it (I wish I had in January!)
On the others then it is quite variable. I can't really give firm advice except to simply watch the market for a few weeks. If you have an investment account then you should be able simply to watch the bid/ask queues for all the ETFs.
The China A50 is generally pretty good, but if the supply of funds from mainland investors drops off for some political reason it suddenly ssems to have no trades.
The Senesex tracker is fine in my experience.
The Bond trackers are very poor. Some days no trades at all.
It really depends on your needs - how long is your investment for, how quickly might you need to sell and so on. All I can say is watch the queues and judge whether it meets your needs.