I am no expert in this area but have dabbled with a modern motor glider from Horizon called the Radian. From what I can tell the Ninja is available from Sig for about $60 as a kit. Probably a good plane at Wingspan 58 in 1473 mm Wing Area 500 in² 32 dm² Weight standard w/16oz(454g) ballast 30 - 34 oz
50 oz 850 - 964 g 1417 g Wing Loading standard w/16oz(454g) ballast 8.6 - 9.8 oz/ft² 14.4 oz/ft² 2624 - 2990 g/m² 4394 g/m² but as a slope soarer I bet the experts would consider it old world because it is balsa construction. And prone to cracking, compared to foam models that bounce. There's really nothing wrong with older designs. A Gentle Lady for example will always be considered a good plane, especially for somebody new, or an expert that just wants simple relaxed flying. So I'm not sure what your intent maybe for a Ninja, but Sig kits in general, built well, will produce nice flying planes. If you ran across a Ninja kit, or are thinking of building one, you probably cant go wrong. Hope the "experts" chime in. They'll give you their opinions. Good luck.