No offence to you bro,and I know shi7 about extended arms (right now,anyway) but that thing looks a little whimpy.
No under-bracing,(some are engineered well enough not to need it forsure.)
The axle adjusters look whimpy and only hold from one way (when tightening the axle bolt yer chain tension will be really hard to get accurate as the axle moves under torque) It will also make getting the axle straight a little tricky.
Good welds don't have air bubbles (holes) in them.
Axle adjuster bolt looks thin and coarse threaded.
Axle looks to be made of thin wall tubing.
Swing arm sleeve bearing looks a little thin too.
How is the chain runner held on.??? Glue?
Those would be some of my concerns. I am after an arm BIGtime,but I'll wait for the experts to chime in.
Extended bikes are usually purpose built for drag racing applications which are usually accompanied by huge horsepower,not just yer standard 180 Busa power plant. This arm might be OK for Friday Night Posing,it just doesn't look beefy enough for hard excelleration.
Hopefully for you...its just my paranoia acting up again.
Good luck with it.