I finally got myself an ESR meter, the Peak Electronics Atlas ESR70. I was using it and it seems like a great piece of kit, but i have found some weird cases with it.

Was checking some GSC capacitors on a old motherboard, ones known to fail without obvious signs of leaking. So bingo it picks up a high ESR on one of the caps as expected (ESR of about 1.6 on a 1000uf), though test the next one it comes up as fine and i think to myself thats odd. I examine that cap closer and it clearly has leaked out the bottom !
So i test the ESR and again and it was within spec.

Now i was testing in circuit, but that did worry me a bit since if the ESR was fine but the cap was definitely failed. The ESR70 cant measure the capacitance in circuit, so i would have to desolder to check the capacitance, but if i need to desolder that kind of defeats the purpose of using the ESR meter.