Okay... Halo B and Reloader B are physically almost identical. The Halo uses eyes to see a gap in its paintball stack, which then feeds to react to it, but there can be problems with seeing certain paint colours I believe, especially with dar colour shells on the paint. The Reloader uses Sound activation and so it hears each time the marker fires and "reloads" hence the name. It will automatically adjust itself to the sound of your marker. I've not heard of anyone having problems with a marker being too quiet for it but I guess it could be a potential issue, but you'd have to be shooting a REALLY quiet marker. The Reloader can also run off 4AA's instead of 6 if you don't need to shoot so fast, saving cash potentially in the long run.
The Rip drive is well worth its cost. If you don't have one and your batteries go, you have no way of shooting at all, as the Halo and Reloader cannot gravity feed like a revi could. - with the Rip you'll be able to tension a ball stack - under the pressure from the spring and shoot off short ropes and stay in the game.
Try the fourms Clasified section if you want a cheap second hand one, or give Jimmy at Warped in Wolverhampton a call
www.warpedpaintball.co.uk a call, he imported some a little while ago at a bit of a discount and might have some left.
Hope that helps