품질： 아주 만족하면서 잘 사용하고 있습니다. 국내 다른 UV 잉크보다 훨씬 저렴하지만 똑같은 성능이 있습니다

This product works for my 7840, and arrived in a few weeks. It has a USB-C rechargeable battery, which is a plus, but also (perhaps) a drawback in terms of battery life, as the plug can become damaged over time, making charging impossible. (Hopefully, even when the battery dies, the product will continue to work when connected to the cable. I say this because I'm still using the previous one for my 7715 without any problems after 8 years.) It doesn't come with a manual, and nothing specific is known; it would have been better to include a manual. The main problem is that when charging with a standard battery charger, neither the red nor the green light comes on, and you can't tell what the charge status is, which isn't a good thing for me. I've tested the product in use, and it works perfectly, and with the chip, both the red and green lights come on (and they could have made it work for charging too). I don't think it's a 5-star product, so I'm giving it 4 stars.