Tom,
How does the Mk6 compare to the Mk20? Sounds like they're comparable amounts of spray and the Mk20 has a metal clip with the added bonus of being available direct from Sabre.
Edit: Think I got the Mk22 and Mk20 mixed up. The Mk22 is closer in size to the Mk6, but only available from police supply vendors. Mk20 is available straight from Sabre, but is significantly larger than the MK6/Mk22