I haven't tried one yet, but having tested the LGV and chatted to Umarex about the spec of the LGU I reckon there's a good chance Tye's right.
With an 88mm stroke and a short transfer port (only 5.5mm), a pretty decent piston seal (more efficient than standard HW and AA seals), and a long barrel these are likely to be efficient straight from the box. The LGV already had a nicely finished spring, well finished internals and a set of well fitting guides, together with a piston with bearings fitted - very similar to a TX.
With all of that thrown into the mix, it's hard not to have a well behaved springer straight out of the box.
All the ingredients are there.... can't wait to see what the cake turns out like.