The obedience lead is, in essence, just an extendable lead.

I personally do not like the Flexi leads as with a strong dog like a Rott, they are easily wrenched out of your hand (lost a few fingernails with this one!).  

A long line is invaluable for teaching your dog the recall but I find the best thing to use is the obedience lead as pictured above, or a horses lunging rein for long distances (we will publish illustrations of this shortly.)

Here we see Keeper attached to the obedience lead.  It is in it's shortest form (about 4 foot).

They do need "working in" - saddle soap is the best product going to soften them.  They are extremely strong and cannot be easily wrenched out of your hand.

Here we see the lead extended.  At full length it can go about 10 foot dependant on the type you buy.