In terms of results with pull-throughs, I'd say 'limited' at best, and horrible at the worst, depending on technique.
By 'limited', I mean some of the points already mentioned, like:
>> a set sharpening angle, which obviously limits just how well your edge will perform and may not adequately meet your needs or expectations.
>> issues created because the edge is bottoming out in the 'V' between the inserts on every pass. This means, if the held angle isn't perfectly maintained, you'll be hitting only the shoulder of the bevel on one side, and scrubbing too far into the apex on the other side on each & every pass. As the held angle varies from one pass to the next, both sides of the apex will suffer for it. The net effect, at best, is that the apex will only get so crisp... and at the worst, the apex will be rounded off severely and very quickly. To me, this would be the single most limiting feature of the whole pull-through v-sharpener concept.
>> grind lines only parallel to the cutting edge. As mentioned previously, grind lines parallel to the edge will deny you the 'teeth' in the edge that are otherwise so helpful to slicing aggression. And if the parallel grind lines are very deep into the bevels of a thin edge, they'll weaken the edge laterally, meaning it'll fold too easily in use. This is a known issue with carbide scraper pull-throughs, in that the edges fail quickly and need very frequent touching up.
And by 'horrible', a lot of that comes down to technique issues, like using too much pressure. Leaning too heavily into it can cause the steel at the edge to be pinched between the carbide scrapers (in devices utilizing them, realizing that some don't), which can literally tear the thin edge and leave it severely weakened. And the damage caused by such tearing would necessitate a lot of additional metal removal at the edge to repair it.
And poor or very bad angle control exacerbates all the edge-rounding issues previously described in the 'limited' description above.
Edited to add:
If you think about the combined effect of the parallel (to the edge) grind lines AND the issues creating edge rounding, that's sort of a double-whammy working against slicing aggression. It always leaves the edge performance disappointing, especially once one has seen the benefits of using other means to sharpen, as on stones. That's always been the biggest letdown to me, every time I've tried a pull-through in the interest of keeping an open mind. I keep coming to the same conclusion, and it's never good.
