I don't think Dave of Dj-1800 should care much about the stealth of the interface as the real originators of the interface as such are makers of DJ Hardware solututions way back in the nities. It's like when Apple and Microsoft quarreled about who had the primary right to interface ideas "lifted" from Xerox. Big deal...not!
 
DJ-1800 is a nice application, but have perfomance problems as do Disco. Both DJ-1800 2 and Disco 2.8.9 gave Audio dropouts both when I loaded the second track to play and in Disco also when I momentarily switched applications. How's that for a nice first encounter? This was on a 400Mhz Powerbook G4 that otherwise run Traktor DJ Studio 2.6.2 as well as Traktor Beatport 1.0 very well. In addition Traktor *sounds better*. It has its own audio engine which helps. AFAIK both Disco and DJ-1800 rely on Quicktime.
 
Both Disco and DJ-1800 should compare themselves to the free Traktor Beatport application (you'll need to register, which is free) as well as the professional Traktor Dj Studio suite. Both Traktor DJ Studio 2.6.2 and Traktor Beatport 1.0 outperforms both Disco and DJ-1800 (but may need a g4). I haven't tried Traktor Beatport on G3 hardware though, nor have I tried Traktor DJ Studio 3.
Even the free Traktor Beatport have keyboard shortcuts. Where are these in Disco and DJ-1800?
 
DJ-1800 has few pluses over Disco as you can precue in many decks and better performance IMHO even on older G3 hardware. But in an audio application, audio dropouts are unforgiveable. Traktor DJ Studio also had perfomance problems before version 2.6 and I told them the same thing back then. Native Instruments listened. Traktor rules!
If you can't afford the real Traktor, even second hand, do yourself a favour and check out Traktor Beatport as well as the alternatives. Use what works for you! For G3 hardware DJ-1800 may work best, but on a G4 Traktor Beatport should convince.
Real-time apps are hard work, but if you can't outcreate a free application you might as well develop something else. I suggest both developers try and improve their apps beyond Traktor Beatport. It sets a standard any DJ app should meet or exceed.