We have tried using the I1 a few times indoors, usually to cut down on the amount of equipment that needs to be lugged around. However, we quickly standardized on the Osmo+Z-axis stabilizer for small jobs and bigger DSLR rigs for higher-end work.
If you're using the stock X3, Tennessee hit the nail on the head; you'll potentially need to do quite a lot of correction in post if you're not bringing your own light sources.
Whether you're using the X3 or X5, I would spend the money to buy an Osmo and Z-axis stabilizer. That will minimize the footprint of your equipment and, with the Z-axis stabilizer, all but eliminate any up and down motion that walking tends to produce.