My TMR for calves is called "triple mix"! The 3-way equal proportions of oats, barley and pea balage seems to give pretty good results as a stand-alone ration, with the addition of a free-choice bale of good quality second cut hay.
What the calves don't clean up in less than 2 days, I take out and dump in the cow's feeder. They think the leftovers are candy! And nothing is wasted.
I haven't done any testing yet but will before fall feeding starts.
I'm not claiming to get optimum gains like one could expect to see with a more finely balanced TMR ration, but I also have no additional equipment and fuel costs, a cost which may be more than offset on larger operations.
When we were feeding straw and other lower quality feeds to the cows, I put it out (free choice) in the bale feeders in the morning and then unrolled good quality hay on the snow in the afternoon so that everyone got equal opportunity at good feed.
It seems to work well in several ways - the cows come in to the yard in the morning for the feeder stuff but spend the afternoon and night in the field where I put the good hay. No bedding required, just some yard scraping on occasion!
With my small numbers, this approach seems to work out well without spending money to gain better efficiencies. There is no doubt that you might be able to utilize low quality feeds better with a TMR mixer but you need much bigger numbers than I have to justify the extra costs.