A bunch of different lamps are pictured on the vendor's site you linked. At the top they show the (out of production) ValeoSylvania XE7. That was a very good performer, and it was mechanically pretty robust, built around a Valeo BiXenon projector used in a variety of high-end vehicles as original equipment. But they made some strange packaging choices so major surgery was often required (hack the headlight buckets) to make it fit. There was also an XE7R and smaller XE5R in this family. Those used reflector optics instead of projector. Beam performance was OK, not as good as the projectors, and the high/low hood wasn't as robust as the high/low cutoff shield in the projector version. These "R" versions, also no longer made, aren't shown on the linked site.
Next, under the weird heading "Xenon-HID Sealed Beam" we see the Sylvania Xenarc X1010 auxiliary low beam set. Out of production for years. Never very good, but can be made somewhat less bad by replacing the nonstandard bulb (bluer but dimmer) with a standard bulb.
Below that, the "Xenon-HID XP6024 Projector fits H6024 and X6024", which is a headlite-shaped toy made in Taiwan by GiantLight (see third item
here). If you get ones that work out of the box, they give passable performance until they fall apart. They also make the car look like it needs a bra. The same Giantlight company makes a range of toys shaped like LED headlights, too.
Below that, the "Xenon-HID X6024 Sealed Beam headlight kit", which was a ridiculously lousy product made in China by a guy who chose the English name "Clutch", puttering in his basement workshop. I'm not making this up. The guy had absolutely no knowledge, equipment, or business making headlamps, but in 2000 a Mexican fast-buck artist in Canada managed to con Sylvania into thinking he could supply them with a complete turnkey range of HID headlamps in standard sealed beam sizes. Sylvania wanted this product to get more people experienced with HID headlamps on the aftermarket side so they would buy more HID headlamps on the OE side when they bought new cars. It backfired spectacularly; the packaging was sexy but the product was garbage. Its performance was much poorer than an aged sealed beam, the lamps didn't fit properly, lenses turned yellow and fell off, etc. The whole range (large and small round, large and small rectangular, plus the X1010 aux low beams) was quietly discontinued around 2005 and remaining stock made its way to other fast-buck artists including brightheadlights-hid and suvlights.com, where it fit right in with those vendors' other Chinese garbage they were selling.
Yup, usually so. Even a vehicle with lousy headlamps (for which no better ones are available) will let you see better if the headlamps are in perfect condition, aimed correctly, and equipped with good bulbs fed by good wiring.
Usually, but in the case of a vehicle's exterior lights we're talking about life safety equipment. Modifications that result in objectively unsafe lighting affect everyone on the road, not just the vehicle owner/modifier. And objective measurement is the only way to answer the question of safe/unsafe; peering at the lights or going for a drive and saying "Yep, looks great to me!" doesn't cut it.