Well erect stretches are part of phase four and I remember RED had a big thread going on something like this and I think he said he had good results with them. They will only be painful if I do it wrong or to hard. Anything can be painful while done improperly.
LJF, they are very hard to get used to. believe me I'm no expert but if you can relax into it (try breathing out and have your body go limp when pulling) you can get a slight separation feel to it. Then try to build upon that. But its gonna be pretty subtle
The constrocted stretches DO WORK and are SAFE but NEWBIES stay the fuck away. It will KILL ya dck, thats what supra and shojii I think were trying to get across, it may have sounded as though they thought the exercise was crap, if so thats their opnion, but I have gained from it .... but STAY AWAY from ittill ya get many months under ya belt.
Consult DLD as the dudes say and do his thing, its safer than myn AT THIS POINT IN TIME until ya gain time under the belt.