I love C# and I frequently have a need for high perf. However, unless you need that high perf, don't use Span<T>. Make your code more readable instead.
Span<T> is safer than ArraySegement<T> as it only allows access to a window of array, rather than full array with a "request" to only look at offset->length
Span<T> is better than Array as it also comes with ReaOnlySpan<T> for a view with readonly array elements; whereas Array is always read/write.
I love C# and I frequently have a need for high perf. However, unless you need that high perf, don't use Span<T>. Make your code more readable instead.