Hey SWIM gets these also, as a standalone drug all they will really do is sedate you. Similar to being slightly stoned and less like a benzo hit. SWIM just took 3x 750mg robaxin and 1mg of subutec (swim has m small/medium opiate tolerance) then smoked a joint. Robaxin acts as a booster for opiates and he says he is feeling a very nice buzz all round. Very chilled out, comfortable as warm from the inside,, some blurred vision and a really nice high without a taking too much of any one thing. So basically they are just OK on their own, but useful when mixing with other drugs, although obviously someone would need to be careful when mixing. That's SWIMs experience anyway.
Hope this helped.