Cycling to work

I am thinking about cycling half way to work and picking up a train for the final bit of my commute. I don't need to worry about any size bike on the train as they are allowed and the Times of my commute mean the train is never packed.

I will only be cycling about 5 miles to the train station cutting through a gravel pathed park for less than 1/2 a mile.

Are fold up bikes any good for 10 miles a day? Halfords said they were but the tyres and frame just look flimsy compared to a hybrid.

Any advice would be greatly appreciated.