If you spend more money lights I wouldn’t spend it on another one of those. Most of the growers using them usually end up with about .5-.75 grams per watt. It’s a 70 watt light, so figure about 35-55 grams give or take. Running multiple plants may help a little, but it’s not going to be a game changer.
With small lights like that you should be sure to keep your canopy under control too. Plants can over grow the lights pretty easily.