I used the sumo supplement earlier this year from about march to the end of may to help maintain the weight on my horse especially after he had a virus. Heres the change in about 6 weeks:
mid april
end of may:
so yes I would say it helped build up his condition back after the winter and his virus.
I have used the "forage and fibre" over the last few months as a token feed after riding my Sec D but more recently upped due to work load increasing - it looks and smells like the dullest feed ever but she seems to enjoy it and does look well on it. It's a complete feed so no need to mess about with chaff, contains no cereals which is ideal for my mare and is a little over a fiver a bag! Have been recommended to use the Sumo if she needs a bit more so will watch this thread with interest....