I assume you're talking about these:
https://silverproject.eu/front-lower-control-arm-adjustable-for-datsun-240z-260z-280z/?currency=USD
They are cheaper then what's offered by about everyone else, and they look cheaper too. Why they went with some welded in tube and bushing is beyond me when everyone else goes with a heim joint.
Unless you plain on doing a lot of very specific tuning and adjusting the length, you're eventually going find a specific length you want, and then you have a arm that basically the same as the stock arm except probably heavier.