I'm a pretty firm believer in good quality tubs at this point, at least in my fall calving program. I've fed (yes, and sold) the ADM tubs in the past, and a couple of years ago we calculated that it was just as economical to feed the complete tubs as to feed 2 lbs. a day of cubes plus a free choice high quality mineral. I used the ADM tubs starting in September, and never had any problems with over consumption. My cows bred back quicker, milked better, weaned bigger calves, and were just overall healthier and looked better. I don't consider convenience to be a huge factor because I (or someone) see these cows everyday, but it does allow me to use a four wheeler sometimes instead of having to drive the much more expensive diesel pickup every day.
Last year I made the mistake of going without them - I fed 2.5 pounds of 20% cubes daily, free choice Moormans mineral, and free choice bermuda grass hay, and over half of my September calvers are going to be late November - December calvers this year. I'll admit that I guess I should've tested my hay - it looked very good, but it seems that alot of last years hay around here wasn't as good as usual, something to do with the very wet year following so many very dry ones.
So this year I'm feeding the tubs again, and everything looks really good and the cows that have calved are cycling very well (we'll start breeding next week). I have switched from the ADM's to Sweet Pro's though - they're costing noticeably less and seem to be working just as well.
Admittedly, I've never tried feeding grain to cows - it's not really common practice around here, and it would require some investment in equipment and facilities that I don't currently have. If those things are available to you though, that might work better for you.
Hay and protein cubes are all I use on my spring calvers, and that usually works plenty well enough for us. I also have a Sweet Pro "Kalf Kandy" tub out for some spring born heifers on grass, and they seem to be doing really well on it, too.