Agreed, sensible prices and good service too. Another great source of heatsinks/boxes is "SourthWestRenewables" on eBay. They recycle the chassis/box/heatsinks from a variety of solar inverters. They usually take an offer too, so save a £'s.
e.g.https://www.ebay.co.uk/itm/134018359225?hash=item1f341ddfb9:g:n8YAAOSwbcJiAlbW which is a copper-coated (spray) polycarbonate box with a big heatsink under. The plastic bit can be unscrewed and the inner part cut out to access the heatsink. I'm fitting big amps for 3.4 and 5.7 in one, plus RX strips.
Gareth