Have to clarify something....the Arresti, as manufactured by ESM models in China, various world-wide distributors is a continuing refinement of a VERY good design by Tom and Bill Bloodworth of Australia.

It does NOT - repeat NOT - come stock with ANY carbon fiber accessories. The stock wing tube and landing gear are aluminum, and pretty heavy. The latest built-up wing version is still right at 5.2kg or so.

To be FAI 'legal', one must install a Carbon Fiber wing tube, Landing gear, and wheel pants.
These modifications bring it to 4.9kg or less, easily.

Forgot to add that using a good CF tuned pipe or muffler ALSO reduces weight. Then lightened backplate spinner, and a few other things CAN bring this airplane to 10 lb 6 oz.
Both of mine started life well over 11 lb, and performed flawlessly. Lighter can be noticed, but doesn't seem to be much of a factor on this airplane. It has plenty of wing.