two things to keep in mind.
1. from my experience, buying none name brand HIDs from amazon/ebay/anywhere else, they are good and bright, but don't last long (as HIDs should). they are a good inexpensive option to start with, but when they go out, I suggest upgrading to a specific brand, PM for the company name & website and I cannot post it here due to forum rules.
2. not sure about your specific model, but if you have HIDs, it is almost a must to have projector housings for whichever bulb has the HIDs in it. if you have HIDs in housings designed for halogen bulbs, you will be blinding everyone coming the opposite direction from you on the road, even without having your high beams on. halogen housings are only designed for so many lumens and as you know see, HIDs highly surpass that number of lumens. I would also suggest to have your headlights realigned, they may not seem off, but with the higher output of light, they may need a minor adjustment
Thanks for taking the time to offer your view.
I've been using HID bulbs in my motorcycles for many years. The single halogen headlight in my 1996 BMW R1100RT was totally inadequate, to the point of being dangerous. Switching to an HID made all the difference.
I had heard all the horror stories about the "cheap Chinese/Taiwanese cr*p", but none-the-less, for my first HID I selected a less expense system based on reviews of actual users. I made sure the bike could quickly be return to the stock configuration if needed. The stock halogen was wrapped up and stored on the bike should the HID system fail.
I installed that HID at about 50,000 miles. When I retired the bike at 175,000 miles the stock halogen bulb was still stored on the bike, I did have one issue along the way: the HID got to where it wouldn't fire off right away. It would come on after a second or so, but it still needed to be addressed. The solution was simple since the kit I had purchased had two of everything as would be needed for an automobile. I didn't even bother to track down if the problem was the bulb or the ballast; I just swapped them both out. So in 125,000 miles of continual usage (motorcycle headlights are always on) that was the extent of my problems.
I've also read all the stories/reports about how the housings developed for halogens will be inadequate/terrible/dangerous/etc. What I've found in real life experience is that with proper aiming the HIDs are far superior to the halogen bulbs they replaced, and they do not blind oncoming traffic when properly adjusted. The most expensive HID bulbs must operate in the same housings. They may have better quality control or components, but there is no way to be sure. Price doesn't always have a 1:1 correspondence with quality/function.
Finally, to clarify, my SLK has factory HID low beams. The high beams were halogen.