The downside is that it's hard to prove if you decide to sell it on (which obviously will never happen) that it's not a neck that you've changed yourself, on a Strat body, and so lower the value, rather than increase it.
The downside is that it's hard to prove if you decide to sell it on (which obviously will never happen) that it's not a neck that you've changed yourself, on a Strat body, and so lower the value, rather than increase it.