I think it depends on your build and power you expect to put into it. I have a vfit air rower but put any decent pwr through it and I end up rocking it off the floor - I'm 90+kg . I go for a run for 1/2 hr, then spend another 1/2 hr on the rowing machine. There's enough to stimulate me with trying to ensure I get certain distance within the 1/2 hr workout. Will prob invest in a concept 2 in the future. Another problem I find with the rowing machine I've got is that kids tend to knock the handle off its perch, and the chain comes derailled from the pulley wheel.. so I have to unscrew covers and re-fit the chain.