The TB DIY frameless 300 x 300 x 25mm HEPAs (25-30rmb ea) or those customised to 285 x 320 x 45mm (rmb 110-120 ea) are ok.
The 25rmb ones would convert the AX40 into a 200 m3/hr CADR min machine, capable of handling our indon haze PM sizes (tested) and also convert the AX40 into a lower dB SPL machine in high speed accordingly.
You will lose that 320 m3/hr CADR capability though. But no issue for those using in the bedrooms, even in a 20 sqm bedroom there is enough airflow for good ACH sufficient enough for say allergic rhinitis sufferers (min of 5x ACH, after factoring in the furnitures).
If one is using the AX40 for the living room of a 4-room BTO, inclusive of the bedroom corridors and main door corridor spaces, then you'd need to use the original Samsung filters.
Either that or change to a Xiaomi Gen 3, but do remember that at 320-400m3/hr CADRs it would still be significantly louder than the AX40, even though they tested the Gen 3 @ 400 to be a wee bit better in SPL than the Gen 2 @ 330.
The main issue now is that Taobao official forwarder (Cainiao) does not really ship these DIY type HEPAs via air ship already. They are forcing you to do sea shipping, and that'd be volumetric weight if i am not wrong.
And most 3rd party forwarders are more than happy to levy half-volumetric charges for such light items, cannot run one unless you are lucky coz you are just shipping 2pcs of 300 x 300 x 25mm and so it's not so immediately apparent to the warehouse workers doing the 入库.
PS. The only issue that some are complaining is that there is a slight smell (plastic) that the TB filter media gives off. This can be solved by airing the filter in lowest fan speed mode for 48hrs before using.
But still some folks find this to be an issue, coz that means 2 "missed" nights of usage.
So those pax would rather go for the originals @ SGD 90 each currently. The originals have activated carbon as well, but then the CADR for formaldehyde (if there is such an issue in the first place) is just 50 m3/hr CADR, not very high for such granulated activated charcoal type. (the xiaomi green one is even lower than this actually).
No issue, all are personal choices
