Mark beat me to it about the hard vinyl on the Cardas LP. BTW, 5 -7 hours seems a very short time for a new cartridge to even begin opening up! About 25 hours has been the minimum in my experience.
As for using a sweep frequency band, such as on the Cardas LP, to break in a cartridge: no, that's a waste of time I agree. All a cartridge needs for break-in is repeated flexing of the suspension to "limber it up"; and any records with a good range of frequencies in the music signal (especially bass) will do.
A little known, but very important (IMO) break-in tip/refinement, especially for low-compliance MC cartridges with stiff(er) suspensions: I always break them in (for the first 50 - 80 hours) with the VTF set at about .2 to .25 gms over the manufacturer's max recommended VTF. Why? Because it's very likely that in normal use (especially with MC's) you will be tracking at or near the high end of the recommended VTF range. So you want to insure that the suspension's AFTER break-in elasticity ("Q" or "K") will extend uniformly/smoothly a little PAST the optimum VTF point you've determined for best sonics, tracking, etc. You DO NOT want the suspension (after break-in) to have two different "Q"s right across the "cusp" of your optimum VTF! Don't worry, adding a little bit of "English" like this during the initial break-in will damage neither cartridge or records. In fact, if you didn't use this little "pre-stress" technique with your MC cartridge when it was new, you can do it any time afterward, and you will get much more stable performance in the future.
The frequency sweep track on many test records while not necessary for cartridge break-in, can be quite useful for cartridge maintenance IMO. While I don't think demagnetizing is an appropriate application for any of the three main cartridges designs (what's to get magnetized??), the process could cause damage, especially to the tiny magnets of MM and MI cartridges. Some demagnetizers (and even some phono-preamps) have also been known to fry the coils of more delicate MC cartridges, such as Jan Allaert's.
On the other hand, running a full-frequency-range sweep signal (especially the very high frequencies) a couple of times through a MC cartridge every one or two dozen plays can help keep the metal coils' crystalline structure uniformly oriented and packed together at the molecular level (similar, though not as completely as cryo treatment.) This will allow more(?) output from the coils, although you may not notice it ;--) And it may or may not 'freshen-up' the coil armature too, depending what it's made of.
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