They do take a bit of getting used to, especially the harder ones - I find more flexible ones like gel inserts more comfortable. I have tried them for inflammation though rather than fallen arches - my ex suffered from flat feel though and he wore them.
He used to be very careful about his footwear and bought from places selling good quality supportive footwear with a decent sole, mainly Sketchers.
When I started getting really bad pain from plantar fasciitis I got some trainers from a sports shot - like fit flop type but a lot cheaper. They have a curved very thick bouncy sole and have made a huge difference. With arthritis I've been a lot more careful about footwear - I even make sure my slippers have a nice soft thick sole so I'm not walking flat to the ground to reduce the pressure/impact on my feet.