For a trackbike, the most important feature is that they are as short as possible!! The longer they are, the greater the likelihood that they will 'dig in' when the bike leaves the tarmac and hits the grass/dirt/gravel at the edge of the track. Something digging in causes cartwheels and crazy damage, and while there's some things you can't get rid of (handlebars, footpegs), you can control how long your frame sliders are. Some racers don't use them at all, figuring that the damage that will be saved by the sliders can be completely outweighed by the possible damage of a cartwheel.
Road bikes don't have to worry about this as much (no dirt or gravel traps to hit), and on a road bike you are trying to protect the expensive OEM fairings from damage, usually from being dropped at low speed or a standstill. But I've seen road bikes that have dented frames from long frame sliders that have fallen off the sidestand!! Long sliders equals a lot of leverage on the bolt going through the frame, too, and frame damage around the bolt hole is also quite common. Offset 'no cut' ones are normally even worse, although there are a couple of designs that are ok (mounting to multiple frame holes etc).
So, if they are very short as they should be, then the issue is that they don't have much plastic to wear down, and you can end up wearing the frame bolt, making removing them very difficult! So you need ones that have a solid puck, not a hollow one with the removal bolt inside.
In short, buy Woodcraft! Nothing else I know of fits all these requirements. They make two puck sizes - race and street, with the race ones being shorter than the street ones.
Here's what they look like (those are the street pucks; the race ones are shorter).
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