I'm not sure why people are ruling it insanely conservatively. It is a half feat, and as written not that strong.
The die you roll (the d10) gets a min roll of (Con bonus*2). You usually then add your Con.
So a fighter with 16 con (+3) has a min roll of 3*2 (6), so heals 9 to 13 HP (usually 9). This min roll is worth a whole 1.5 HP per HD rolled.
On a 1d6 HD, you heal 9 HP per HD.
Amusingly, if you have 20 con, your min roll is 10 - so a d6 HD heals 15 HP, as does a d10 HD.
This is "worth" (con bonus*2)(con bonus*2+1)/(2*HD max) extra healing per HD so long as you don't over-shoot your HD max.
In comparison, a bare +2 con is worth 2 HP per HD (+1 max HP, then 1 extra when you expend HD). Even with this generous interpretation, Durable only gains marginally more HP than increasing con, and you lose out on con saves and con checks (etc).
The die you roll (the d10) gets a min roll of (Con bonus*2). You usually then add your Con.
So a fighter with 16 con (+3) has a min roll of 3*2 (6), so heals 9 to 13 HP (usually 9). This min roll is worth a whole 1.5 HP per HD rolled.
On a 1d6 HD, you heal 9 HP per HD.
Amusingly, if you have 20 con, your min roll is 10 - so a d6 HD heals 15 HP, as does a d10 HD.
This is "worth" (con bonus*2)(con bonus*2+1)/(2*HD max) extra healing per HD so long as you don't over-shoot your HD max.
In comparison, a bare +2 con is worth 2 HP per HD (+1 max HP, then 1 extra when you expend HD). Even with this generous interpretation, Durable only gains marginally more HP than increasing con, and you lose out on con saves and con checks (etc).