General preference seems to be for .209's as they are still highly effective while being far more cost effective. In addition to this the overwhelming majority of sites are perfectly happy with .209's but usage of 9mm can be very hit in miss in terms of sites allowing them and even fewer sites allow mag flash's. Mag flash's appear to be rarely seen outside of dedicated events such as milsim events.
A lot of this is down to health and safety restrictions and insurance restrictions.
While these grenades aren't banned it simply falls down to demand which is invariably effected by any limitations in place. Dynatex are by far the easiest to obtain and they have the ability to use all the blanks previously mentioned, when used with the appropriate adapter. There is also the Alpha Tec Hex but I'm not sure what size blanks this uses. As far as I know the TRMR is no longer in production.