Hey,
Glad you like your log vape.
For the most part, the prefilled cartridges can be considered safe, as they are supposedly lab tested for residual solvents/contaminants. This is not guaranteed though, so always do your own research before buying anything. It is certainly safer than just vaping a random nug which you have no idea where it came from/how it was grown though. So... it's all a matter of perspective I suppose.
Referring to your topic question.... there are so many different pens these days... Lets start with wax pens:
Basically the two main types of wax pens are:
First, either a coil or pancake that heats up and cooks your wax. These will vaporize/burn your wax when directly added in, small bits at a time. There are also some fancier versions that will hold a lot of wax and slowly release it into the coil:
https://www.vapornation.com/persei-vaporizer.html (A lot of folks seem to either love or hate this design though, mainly due to the super tight draw restriction.)
The second main type of wax pen would be a tank style. This would mean you are thinning your extract with PG/VG/PEG, terpenes or a CO2 extraction so that the viscosity is such that your tank can wick it up. Be warned that there is some hesitation in using these thinning agents, in regards to how it can impact health:
http://fuckcombustion.com/threads/ejuice-mixes-vg-pg-safety-journal-article-inside.22290/
http://fuckcombustion.com/threads/pg-update-toxic.24198/
On to Dry Herb pens:
Mostly... no. A lot of these options just have a coil that heats up and combusts your herb. I.e. The Megatoke.
There is the Grasshopper though. This little fellah is powered by a minituarised heater which is 3d printed. It is capable of achieving the same power as most desktop units but in a convenient pen-like form. There is a lot of hate for this device regarding it's reliability though. (
https://www.grasshoppervape.com/)
There is also a neat project in development called "The Splinter," by RastaBuddhaTao:
http://www.rastabuddhatao.net/projects/splinter
This is supposed to be a dry herb atomizer that you can screw into any 510 threaded mod box (what powers atomizers that most vape pens use). Looks intriguing to say the least, but this may or may not come out this year, and it is tentative imo if this will come out next year either.
So things are developing on the dry-herb front, but not quite there in penlike form.
Well.. hope I helped, and didn't confuse more. That's my little overview of pens at the moment.