I have used AP 4 pots whilst working at 2 previous companies & they are very good with no issues whatsoever, agreed.
I am also aware of HiSpecs reputation over the last 10 years or more & appreciate that they have been known to be very slow to deliver orders to private individuals. I have also seen a couple of calipers a long time ago which had fluid leaks from new (quickly rectified though). However I think that as the company has grown over the last decade they have refined the product, ironed out the teething issues & improved the customer service.
I can only comment on them now & can honestly say that I have had nothing but A* service over the last 3 years & they are genuinely up there as one of the best suppliers I have. Their calipers are well finished & well presented & offer excellent value for money. They deliver on time & the customer service has been excellent.
Radical also use a lot of their products so I assume that they must offer a decent level of reliability.
I also agree that if I was building a 1000kg plus GT or circuit race car I would have probably gone to AP or Alcon too but for a fast road/trackday car then I am more than happy to endorse the Hispec product.
I would also like to add that they have a new caliper range out which hasn't made it onto their website yet called the RX range, these are competition based calipers (so sans dust seals) which have a stiffer body to prevent flex & certainly do look the part & look more akin to the AP or Alcon type of caliper.
I would also suggest that the choice of friction material is important relative to the application the car is being used for.
Just my opinion of course & everyone is entitled to their own view but no complaints from me.
As they say, you get what you pay for.