I've Koolstops on most of my bikes. They last, don't eat the rims, brake well, and last.
On my Dave Yates (caliper brakes) I've had salmon inserts on for yonks. I can't remember when I fitted them, but it's a high-mileage audax bike which gets used in all conditions and they must have been on there for a couple of years.
Don't get the Koolstop holders, though. They are utterly rubbish. There's about 1 mm of metal to tighten the holder onto the brake, which rounds off as soon as an Allen key is in the same room. I use the pads in some other holders (probably Shimano or Tektro).
On my tourer (v-brakes), the front pads (black Koolstops - I couldn't find the salmon ones) have lasted at least 12,000 miles and possibly 15,000. They're still on there. The rears don't last as long - I fitted a new set in Istanbul and replaced them when I got home, so about 7,000 miles.
I did try some Asda blocks on the rear, which braked well and didn't eat the rims, but they needed replacing after less than 2,000 miles. They also come as a full unit, so replacing them is a bit more fiddly than just swapping out a couple of pads and pins. There's also a slight weight penalty if you want to carry spares.
I haven't noticed the squealing issue, and though six or seven quid for some moulded rubber seems a bit daft, they are economical and effective. I'll keep using them.