After testing the WANLIAN lock stopper for weeks, I can confidently say it's a solid childproofing tool – with one major caveat. The aluminum alloy body feels surprisingly sturdy in hand, and the rubber coating truly prevents window scratches (no more cringing at metal-on-glass sounds!).

The hex key adjustment system is genius – I could set my balcony door to open just 4 inches for fresh air while keeping my toddler safe. Unlike bulky security bars, this discreet little gadget disappears into the track when not in use. Installation took literally 10 seconds – no tools needed beyond the included key.

However, be warned about vinyl/aluminum tracks: When I cranked it tight on my patio door, I noticed slight track bending. It still functioned, but I wouldn't use it long-term on softer materials. Works perfectly on my steel-framed bedroom window though – that thing isn't budging even during storms!

The adjustable width (10-60mm) accommodated all my windows except one vintage narrow-track casement. Pro tip: Measure your track thickness before buying! While some reviewers complained about flimsiness, mine held up to aggressive shaking tests – just be sure to fully tighten with the key until you feel firm resistance.

Final verdict? A+ for security on sturdy tracks, but potentially damaging to softer materials. For $12, it's cheaper than most child safety locks and does double duty as theft prevention when traveling. Just don't expect it to stop determined burglars – this is more about preventing accidental openings.