Dakkot (Thin Ones) - These are made by stretching a thin layer of parchment over a structural base similar to the peshutim. This outer parchment forms the entire box of the tefillin, including the inner as well as the outer walls and also the base, which is halachically desirable.
Kosher and proofread by an expert proofreader. Comes with a computer check certificate and a certificate about the kosher level.

Ktav Beit Yossef or Ari?
The most common script is called beit yosef since it is the form prescribed by Rabbi Yosef Caro in the Shulchan Aruch - the primary work of Jewish law. However, the great kabbalist Rabbi Yitzchak Luria Ashkenazi promoted a script that differs slightly from beit yosef script in nine letters of the alphabet. This script is called ktav ari - ari being the Hebrew acronym for Rabbi Yitzchak Luria. Most Ashkenazi, non-hassidic Jews, as well as most Sephardi Jews, use the beit yosef script, while most hassidic and kabalistically-oriented Jewish communities use the ktav ari script.

Ashkenazi Beit Yossef - generally used by those following Ashkenazi tradition, from Germany, England, Russia, Lithuanian

Ashkenazi Ari Zal - generally used by those following Chassidic Sefard tradition, from Poland, Galicia, Hungary, Romania, Slovakia

Right or Left Handed:
If you are right-handed you wear the Tefillin on the left arm whereas if you are left-handed you wear the Tefillin on the right arm.

Hand Strap Wrapping Direction:
Inwards - Beit Yossef, Most Ashkenazim wear the knot to be tightened (not to be confused with the knot on the base which is permenently tied and always worn on the inside, facing the heart) on the inside and wrap inward.
Outwards - Ari (Nusach Sephard) Ashkenazim and all Sephardim wear it on the outside and wrap outward.