I can't find any easy info on the threading of this device. It LOOKS like an 808 thread, which means you SHOULD be able to buy better/larger 808 cartos for it, but without knowing the specific threading I can't say. Buying empty cartomizers (even their branded ones) and filling with your own liquid is always gong to be more cost effective. I will say from personal experience using smaller cig-a-likes, the battery life between charges may not be sufficient. It comes with a PCC charging case, those are pretty much essential for these smaller devices, start the day with the case fully charged and you should be okay long enough to get to a USB/Wall socket to recharge it if required.
All that out of the way, there's absolutely nothing inherently wrong with smaller ecigs. Many people, myself included, started on them and managed to not smoke while using them. Every device has pros and cons. As long as it's meeting your needs there's no "need" to go buying another kit right away. Some of us end up doing it because we wanted more from our vape (I ended up upgrading after finding ECF and discovering that there was so many other devices to choose from, I had no idea). Some of us get obsessed with trying all sorts of liquid deliveries/battery combinations. It's a personal thing that only you can decide for yourself. If you decide to get another kit, you'll probably want a 510 threaded device. The amount of options after you have the first batteries are astounding.
So, in summary, I see nothing wrong with this PV. If it works for you then that's all that matters. If it isn't working don't toss all ecigs out the window, there's definitely more viable options out there that will most likely satisfy your needs.
Oh, and welcome to ECF! There's a lot of knowledgeable people here, and it's a huge resource of information. Pretty much any question you have can/will be answered.