below about 15 you should evaluate him without giving effect to any growth - do you want him as he is right now? if so, then great, he will improve some but not much.
At 5, good chance that offseason regression offsets skills improvements the first season. Slow slow slow improvement.
BUT, such players can be great signings. Some folks dont even look at guys below a certain WE - I think it is wise to look at them.