Since they only mention "Singapore Post Airmail" it's hard to say whether or not it's registered. It's a gamble, as far as I'm concerned!
Personally, I've had a great experience with 'China Post Registered Airmail' shipping method so I see no reason why one should choose a questionable shipping method over a proven and 100% reliable one.
'AliExpress Standard Shipping' is another very reliable method, more reliable than 'CPRA' I'd say because AE itself monitors the parcels and is responsible for their delivery to the recipient. Whereas one time I ordered some stuff via 'CPRA' but the seller instead sent it to me via 'Ordinary Small Packet Plus', which is unregistered, yet charged me the extra fee nonetheless.
Hope it helps.