For amps and speakers, it is alright to source from overseas if you know the seller well.
But for HUs, I suggest you source them locally although the local price is a little higher.
The reason is that HUs, unlike amps and speakers, involves a lot of moving parts and is subject to wear and tear.
One good example is the pick-up lens which at best last no more than 5 years.
If you bought the HU from overseas and if the lens gone kaput, it will be very difficult to get the local shops to service it for you.

If you buy from those parallel importers, I don't think they will attend to your problems, esp if it is after 3 years or more.
If you buy from installers in Singapore, then perhaps they will arrange the repair for you.
Having said that, it is always better to make things clear with them before the purchase.

In my experience, ICE equipment in UK is quite pricey due to the VAT.
I came across an Xtant 4 channel amp in Sim Lim SQ (Edison) selling for S$780 (about RM1,850) which I think is quite a good buy, considering the amp is made in the States.