Sure, you'd like to think... But no, cost does not always equate to quality. Sure, Guarder might have gotten a bit better over the years or some people might have gotten lucky with a well made kit, but that's not always the case. For example, you'd have thought drilling the hole for a 1911 dual safety selector would be an easy thing to align, but nope, not for Guarder. Again, that's not to say it was bad on every kit, but at least the one I did was.
Providing it fits and works, you should be able to use the plastic outer barrel. But when you have a metal slide, it will be the plastic parts or the weaker metals that will wear down, not the slide. So if there's any rubbing etc, it will reduce the plastic down or simple grind past it. On the flip side, if there's an ill-fitted metal outer barrel, you will need to take a lot of time and care to make it fit right - it's the one upgrade part I hate fitting in metal kits as there's a lot of movement and any badly made parts will stand out by simply jamming up the slide.
Mind if I ask what the goal of the full metal kit version will be for? If it's purely for show then it will matter less, but if it's for cold weather skirmishing I'd personally stick to full plastic - but those are probably not your answers.