Unless you need to be able to change the deleter at runtime, I would strongly recommend using a custom deleter type. For example, if use a function pointer for your deleter, sizeof(unique_ptr<T, fptr>) == 2 * sizeof(T*). In other words, half of the bytes of the unique_ptr object are wasted.
Writing a custom deleter to wrap every function is a bother, though. Thankfully, we can write a type templated on the function:
Since C++17:
template <auto fn>
using deleter_from_fn = std::integral_constant<decltype(fn), fn>;
template <typename T, auto fn>
using my_unique_ptr = std::unique_ptr<T, deleter_from_fn<fn>>;
// usage:
my_unique_ptr<Bar, destroy> p{create()};
Prior to C++17:
template <typename D, D fn>
using deleter_from_fn = std::integral_constant<D, fn>;
template <typename T, typename D, D fn>
using my_unique_ptr = std::unique_ptr<T, deleter_from_fn<D, fn>>;
// usage:
my_unique_ptr<Bar, decltype(destroy), destroy> p{create()};