With the AD999 be sure it's the 900ms of delay time you want, because in my opinion the tone of the repeats is not superior to other analog delays I've tried. I used to have a 70s Ibanez/Maxon AD100 desktop delay, which is more or less an vintage Ibanez AD80 pedal in a box. Perhaps because this unit is running at a higher voltage, the repeats were thicker and more punchy compared to the AD999. As a percentage, maybe 15% better. That said, I'd always take the AD999 over the AD100 as it's a foot pedal, will run on 9v, is true bypass, and has 3 times the delay time of the latter unit. 15% better tone does not come close to outweighing these advantages. The AD999 is still a fine sounding unit, probably equal in quality to other lauded 9v delays like the Boss DM2/3 or Ibanez AD9. If you're only interested in slapback a higher voltage Ibanez AD80 might be a better bet. But keep in mind that the AD999 can do everything the AD80 can do, but not vice versa.
There's a bit of hiss in the repeats of the AD999, especially at longer delay times. This is probably a consequence of analogue delay being stretched out to 900ms, when the standard is 300ms. It's not overwhelming and is to all intents and purposes inaudible when playing, possibly unless you have the delay level maxed and you really let the repeats ring out, and even then in a band situation you could be sure no one would hear it.
This unit will self-oscillate. Crank the repeat knob and use the delay time to control the pitch of the oscillation.
It feels pretty solid. For the price these command I hope they're made well. Maxon have been in the business since the 70s (Ibanez effects of the 70s and 80s are just rebadged Maxon effects) and many of the units they made back then are still kicking.
With 900ms of analogue delay this pedal is unique in the marketplace at present. Even at US$340 new I think these pedals are priced fairly. People are going crazy paying AUD$300+ (US$230) for a vintage Boss DM-2 off of ebay that will only do 300ms of delay. Used, these units can be had for not much more than the Boss (or in my case, slightly cheaper) and they offer so much more. Another comparison: the EHX Deluxe Memory Man has recently had a price increase to around US$310, at it's huge, has sketchy build quality, needs its own power supply and only has 550ms of delay. Although not the best sounding analog delay I've had, the AD999 is overall the best analog delay I've owned. I doubt I'd buy a different delay again (I'd begrudgingly buy another if it were lost or stolen). It'd be great to be able to say the same thing about overdrives.