Did you check out their website? It looks like a legitimate operation, but that doesn't mean it's a good idea to follow through with them.
First - exactly how big do you want to grow your pen making business? Are you aiming for the stars or just doing this in your spare time or retirement? Because there's really no point listing your products on walmart.com unless you have the intention to sell dozens of sales per week, you might as well stick to Instagram, Facebook and Etsy for a handful per month.
Second - what percentage of your sale price are you willing to hand over to them as commission? They surely expect to be paid for whatever service they provide to you, and it will either be in the form of a percentage or it will be a flat fee, which could leave you making a significant loss if your sales don't live up to expectations.
I'm not suggesting this is wrong for you - I don't know your situation or plans and aspirations. Just go into it with your eyes open and be careful to avoid getting stuck doing something you didn't bargain for and don't enjoy.