Public Sub Main()
    Dim a As String, b As String, t As Single

'    a - входная строка
    a = String( 10000000 , "a") & "home"
'    b = строка для сверки
    b = String( 10000000 , "b") & "abcdefghmopuyt"
    
    t = Timer
    Debug.Print MyFunc(a, b), Format$(Timer - t, "0.0000")
End Sub

Public Function MyFunc(a As String, b As String) As Boolean
    Dim ma( 255 ) As Boolean, mb( 255 ) As Boolean
    Dim i As Long

    For i =  1  To Len(a)
        ma(Asc(Mid$(a, i,  1 ))) = True
    Next i
    For i =  1  To Len(b)
        mb(Asc(Mid$(b, i,  1 ))) = True
    Next i
    For i =  0  To  255 
        If ma(i) Then
            If Not mb(i) Then Exit Function
        End If
    Next i
    MyFunc = True
End Function

    '    a - входная строка
        a = "home"
    '    b = строка для сверки
        b = "abcdefghmopuyt"

Option Explicit

Dim ms( 255 ,  255 ) As Boolean

Public Sub Main()
    Dim sb As String

    Dim m() As Byte, i As Long, j As Long, b As Boolean
    Dim a As String, t As Single, ma() As String

    ' Строка сверки
    sb = "123456789"
    ' 1000000 сверяемых значений
    ReDim ma( 999999 )
    For i =  0  To  999999 
        ma(i) = CStr(CLng( 1000000  * Rnd))
    Next i

    t = Timer

' ------------
    ' Заполним матрицу сверки
    m = sb
    For i =  0  To UBound(m) Step  2 
        ms(m(i), m(i +  1 )) = True
    Next i
    ' сверим наш миллион значений
    For i =  0  To UBound(ma)
        j = j - CLng(CompA(ma(i)))
    Next i
' ------------

    MsgBox "Есть все симоволы в " & j & " из " & i & " за " & Format$(Timer - t, "0.000") & " секунд"
End Sub

Private Function CompA(a As String) As Boolean
    Dim m() As Byte, i As Long
    m = a
    For i =  0  To UBound(m) Step  2 
        If Not ms(m(i), m(i +  1 )) Then Exit Function
    Next i
    CompA = True
End Function