Cheap clip-on lights can't compete with dynamo lights for regular use, nor with powerful rechargeables for light output. But for occasional use under streetlights or as get- you-home backup lights, they're fine.
Now that LEDs have usurped filament bulbs, they even last a fair while - up to 150 hours (flashing) for this two AA- powered single-LED front light. The two AAA-powered three-LED rear lasts up to 200 hours - again, flashing. Both have constant modes as well, in which the front lamp throws an oval pool of crisp light far enough ahead of your front wheel for the darker bits between streetlights, although illumination isn't really up to country lane use - unless you go very carefully. There's a lens halo around the LED that's visible from the side, albeit not very brightly. The rear lamp is visible from most of the rear quadrant but only bright from directly behind.