Strictly speaking, penstyles are dead and gone. Only models that are exactly like pens, such as the DSE801, are penstyles. They are slimmer than the eGo type. There are very few vendors of these old models now, one is called the V8. Like the superminis (which were even smaller versions of minis like the 510), things have changed. Micro batteries like this are called 'shorties' now, and models that exclusively use those shorty batteries (and generally with weird threads too) are virtually RIP.
What we have now are:
- Minis (510, KR808 etc) - also called cig-alikes or looky-likies. You can get shorty batts or XL batts.
- Mid-size (eGo, kGo etc) - also called fat-batts. 650mAh to 1300mAh batts.
- APVs: mechanical, basic electrical or electronic; boxmods and tubemods - also called mods. Most have user-replaceable generic batteries.