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I sandwich the strip between the back halves because it is faster, and the fit should be as good or better that an inlaid strip (clamped plates with jointed edges facing the strip vs. an inlay). The cross grain reinforcement is what gives the joint its strength, I don't believe the minimal amount of long grain wood under the strip does much for the joint one way or the other.

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Rian Gitar og Mandolin

(selective quote again)

I think, like alot of things the execution is more important than the actual method. I usually sandwich, but had one client who decided he wanted a back strip after I had joined the back. I clamped down a straight edge to guide my router.

For back (and top) joints poor joinery usually results in a crack, right next to the glue joint, not along the joint, at least that's they way most center seams cracks I've seen were. If it comes apart at the actual joint I suspect it was a gluing problem. I use HHG. It's hard to get a sandwiched joint together before the glue jels, at least for me. I just apply glue, assemble and clamp, even if it's already jelled, then heat it with a heat gun to reactivate the glue.

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I didn't mean to say it, but I meant what I said.
http://www.brackettinstruments.com/

I would say the ones I noticed movement on were made as well as humanly possible. I was actually doing it in 2 stages. I jointed a back half and a side (because I couldn't figure out how to perfectly straighten a narrow flexible strip to perfection) and had the bwb purfling sanded on a granite plate. Glued it, and then sawed off the side with the needed strip remaining (see pic).
Jointed and candled again with the second back piece, added carefully sanded purfling in between. All clamped tightly with a rope and wedges jig.
Later I noticed some tiny shellac fractures here and there on 2 guitars and that was enough for me. The ones I inlaid (and could inspect later) look perfect even if the glue lines are surely thicker and varying (depending on how well I could straighten the flexible center)

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Build log

In the end it seems there is little escape from getting shellac fractures and witness lines over conflicting grains and densities once the guitar ages a bit. This Romanillos rosette is a perfect example of the effect went over the average and I could up with 50 other examples.

What I found out so far is that thinner inlays and thicker glue lines (not visible, just light clamping as opposed to ultra tight, starving pressure with mosaic) reduces this effect to an acceptable or almost invisible level.

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Build log