Last year Fine Woodworking ran a test on these style of "lunchbox thicknessers". Amongst other criteria they measured snipe and parallelism.
DeWalt 735X Snipe 0.003", Out Of Parallel 0.000"
DeWalt 734 Snipe 0.002", Out Of Parallel 0.000"
Makita 2012N Snipe 0.003", Out Of Parallel 0.002"
Rikon 25-131 Snipe 0.002", Out Of Parallel 0.008"
Triton TPT125 Snipe 0.101", Out Of Parallel 0.010"
Delta 22-555 Snipe 0.006", Out Of Parallel 0.008"
Craftsman 21758, Snipe 0.012", Out Of Parallel 0.019"
Anything below the Makita might be fine for basic site joinery, but IMO, isn't accurate enough for precise work.
I know these aren't necessarily brands you're considering, but I'd have thought an application like segmented turning would require very precise components. I guess the message is buyer beware, portable thicknessers exist to serve very different users with very different requirements.