I have raced for years using 4 scales but finally went back to my tweak scale.
I found it was hard to level the area the scales sat on while at the track. The nice setups had 4 scales mounted to a board with a level in the center and screw feet at each corner to level the board before you set the car on the scales. This is nice but not nice to carry around. I have used other guys scales and when I put my car on and then turned the car around the reading differed... also it matters on some scales where the wheels sit... a little off to one side and the reading changes. Also the batterys have a tendency to go dead at the worst times
Since I race XRays I get my car balanced with the XRay balance posts when I build the car and then spot check the tweak before every run on the tweak scale.
A good tweak scale comes in its own box... very small and easy to pack... has no batterys to go dead... is easy to level and use at the track and it is as accurate as you will ever need. But if you feel you need scales they will get the job done if used correctly