Hey Carpfinder.
Basically, a Baitrunner is a coffee grinder, although, there is one very important difference.
In terms of working it, there is very little difference between a bait runner and a traditional grinder. However, the bait runner does come with a latch, on the back, wich can be used to activate the "bait runner" feature.
When active, this feature allows the spool to be totally free moving, in other words, it spins with no resistance. This does not affect the drag setting on your reel however.
What this means is that you can have your drag set ready to fight a fish, but then activate the bait runner feature, and the spool will spin freely, regardless of how tight you set the drag. This means the fish can take line freely with no resistance, but when you hook it, and you de activate the bait runner(many reels do this by themselves when you wind line in), you will have your pre set drag ready and waiting to fight the fish.
An interesting fact is that "Bait Runner" is a trade mark of the Shimano Corporation. These reels were not designed for carp fishing, but rather for fishing with live baits. The puprose of the "Bait Runner" feature, was to allow the live bait to swim as it please, resulting in a very natural presentation.
Carp fisherman discovered that these reels generally speaking have a very good line capacity when compared to normal coffee grinders of the same size, and then adopted them.
Another great thing about the bait runner, is that because the reels gears get de activated when using the bait runner feature, they lend themselves excellently to the use of the "bolt rig", wich has been discussed on here before.
Since "bait runner" is a trade mark of Shimano, most other brands call themselves bait feeders. I have three Okuma Travertine bait feeds/runners, matched with three Penn Powerstick Pro Carp 13ft rods.
The Okuma's are great value for money. I use the "50" size, and they hold 500m of my chosen line. I would really say, rather spend a bit extra, and get yourself bait runners if you are serious about fishing for big carp.
They retrieve much faster than center pins, and for this reason alone are worth their weight in gold when fighting a big fish that wants to get into the weeds or structure.
The Shimano's are fantastic reels, but are alse very expensive. I got my Okuma Travertine's at R270.00 per reel. They hold much more line than the Shimano at the same price range, and are super smooth.
I hope what I said makes sense, and that you have a bit of an understanding of what the reels do, and why they are so important to specimen anglers.
If you need more help, just give me a shout, I'm no expert but I have done a lot of research on this topic when deciding which reels to buy.
Tight Lines,
Jared