Hi Jawine!
The TT protectors in your link appear to be mostly to blunt the ding-causing effects of handlebars striking the top tube in a fall (I really like the one that is made from stainless strips, silver-soldered on; I've done a few twisted-spoke wheel builds like that as well).
'Round here, single-speeds and true Fixies are all the rage with the Uni crowd, and it is increasingly common to see the ones parked in racks sporting a length of foam pipe lagging snapped onto the top tube. I asked one fellow about it, and he said the "nice ones" get nicked so readily while parked. The ones adapted from pipe lagging are so common as to have no theft-incentive. He'd wrapped his with colored vinyl electrical tape to match his frame paint. It looked good from a distance, 'didn't see it up-close.
Ah, me; one more thing to think about when leaving a bike locked but unattended, I suppose. For my money, a TT wrap is bound to keep things looking nice, but I'd apply one only after a thick coat of wax and I'd check it periodically, as I suppose moisture or grit trapped beneath could eventually cause problems akin to long-term use of a protective vinyl "bra" or "mask" on the front of a car.
EDIT: I have a strip of matte black windshield trim tape affixed invisibly to my matte black Nomad's top tube. Works nicely for preventing scuffs when dis/mounting, but would be very noticeable on your lovely yellow Gazelle. I like Alfie's approach. If you applied an "owner's name" sticker beneath the clear tape, it would be a task for a thief to peel it off, making identification easier in the event of theft/loss.
Best,
Dan.
