I've always shipped direct, as their shipping fees have always been reasonable (esp if you compare the total cost, vs buying locally); I'm not sure if you would save much using a forwarder - most of the time when I used one, the shipping fees are quite a bit more due to volumetric weight calculations, rounding up to the next 0.5kg weight step per package, and in some cases US taxes depending on where the receiving warehouse is located.
That said, if you're buying a cpap machine, I would think having it pass though fewer hands would be better - after all, it is fragile/sensitive equipment (masks, and usually, humidifiers are not); also, just in case it is damaged, and neither shipping party would acknowledge being responsible for it. Might also make RMA returns (warranty service) a little easier if you ever need it. Also, I would think, if there are any problems with the import, you may have the option to return it for a refund (possibly with a restocking fee); but it may not be possible if it arrived though a forwarder (as customs will only return it to the sending address, and the forwarder might refuse to accept and return it to the seller on your behalf; or you would have to pay them to do so, if they are willing to).
I would also be concerned if the forwarder would be able to declare the item correctly (which might affect import clearance to SG); if the forwarder would even accept the package (because it is Rx only - check their shipping restriction lists); and if the retailer can accept your (non-US) prescription for shipping to a US address - it could be possible to work around this last point, by paying a little more and getting a mask in separate parts (eg, frame and headgear separately) as doing so usually avoids requiring a prescription in the US; but it is unclear if such a the shipment will be permitted into SG without a prescription.
But yeah, if you do decide to go down this route, do share with us how it worked out, and which forwarder you used.
You are using the 10% discount code with 1800cpap right?