I think that the use of a CRC is not necessary for short frames (say 6 bytes long).

However, very short frames must be avoided, except if you repeat them several times (and this way they are not short anymore).

I use to add a 'unique' header (service identifier) of 4 bytes at the beginning of my frames, and a checksum byte (adding modulo 256) at the end. This is a reasonable protection for general application commumications. I have used this approach even in UHF radio communications.