its not just straightness a small knock could deform the inside of the leg, it might not be visible on the outside , but when you slide the tube in it will jamb or not slide smooth.
If they are cheap enough or you like a gamble go for it.
it is just something to think about
f4/f4i are exactly the same. However, my advice is to not buy tubes without the lowers. The lowers were removed for a reason and you cannot test the components without the lowers on (that I'm aware of).