Hand walkouts are similar to ab wheel rollouts, but you don't need a gadget to do them. The eccentric or lowering portion of hand walkouts is much slower and more controlled than using an ab wheel, so you'll be less inclined to tweak something. Walkouts are also self-limiting in the sense that you can only really walk out as far as your core can control, so you aren't going to find yourself out beyond your level of capability.
Since these don't require any equipment, it's a great option for when you can't make it to the gym. You can also do them from the knees if the standing version is too difficult. Not hard enough? Add a weight vest.