I load 5 rounds in the 6-rd speedstrips I carry for my 5-shot .38's & .357's.
That "extra" 6th round is only going to end up in evidence when it's collected from the ground, still in the speedstrip, which is where I'll drop the speedstrip after loading 5 rounds into 5-rd guns in a situation that merits reloading a snub. Just like I trained to drop empty speedloaders when training & qualifying with service revolvers many years ago.
The extra space does help with controlling the speedstrip during loading, too.
If I'm going to pull one of my 6-shot revolvers from the safe, and I'm not going to be carrying speedloaders, then I'll use speedstrips filled with 6 rounds. I used to keep a couple groups of speedstrips for off-duty revolvers, separated by caliber/capacity.
Manipulating & using speedstrips is a skill that requires some learning and periodic practice. Ditto speedloaders, for that matter.
Speedstrips have a minor advantage in that speedloaders require clearance of the left grip stock to align and insert the rounds into the charge holes as a group. Some grip stock/loader combinations might have clearance issues.