Yes I know... rollers and spin bikes are much better but this is what I have and I don't think the wife will agree we need any more bikes. 5 real bikes and 2 exercise bikes are all we need. So, for the last two days I've experimented with just riding said exercise bikes for 80 minutes at 4am. This is compared to my usual 30km flat course that I finish in 70-80 minutes. Sadly its getting too cold out for me ride before the sun rises so I needed an alternative. Also riding 12000km in 8 months on my nice bike is starting to cost in maintenance - more than I really want to spend at the moment.
From my limited comparison the effort required seems to be similar (if you adjust the tension knob every now and then to simulate going up or down). All I really want to do is keep my calorie output as high as I usually do and keep my legs in shape for daily commuting and the long weekend rides I fully intend to continue all year.
So... other than the sheer boredom of it all (I love downloaded series... makes it somewhat interesting and I can watch my way through them and exercise at the same time) are there any real downsides?