Exercise equipment for someone with dodgy knees

[RiverCityFan]

I have been using an exercise bike as part of a six week course of NHS physiotherapy for my knees.
I was thinking about buying one for home but wondered if a cross trainer would give me a better all round workout.
I need something very low impact on my knees but need to improve my overall fitness (and the bar is very low!) so which would be better-
Exercise bike or Cross trainer?

I think it’s down to personal preference - I find my posture is better on the cross trainer so I don’t stress my back as much, so that’s what I prefer obviously!

Can you go to a gym and try them out to see?

I find cross trainers uncomfortable as I find the feet are too far apart on most and they out pressure on my knees.
Rowing machines were good for me though.

I was about to rent a Concept 2 Rower for approx £44 per month for 3-4 months (they cost £800-£1000 to buy) as a bit of a try before buying. I then discovered Lidl selling a very similar machine (OK, it's not a Concept but it's a dam good copy!) at £199, 3 weeks in and it's going well. They may well still have some in stock.

Thanks everyone. Great idea to try out the equipment at a gym first. I could cope with the embarrassment of exercising in front of others for an hour I'm sure!
I hadn't considered a rowing machine so will try that too and check out Lidl