First thing to the rider on this horse: Take that tie down OFF! It is too tight for one thing, and I don't think that horse needs it at all.
For first impression riding/training things, I don't like how they have worded things in the ad on DreamHorse. Something about it just makes me question the horse. Can't quite pinpoint what it is, but something bugs me about the ad. And as others have already pointed out, the rider can be doing much better for this horse. With those things considering, you could have a few bad habits on your hands that are going to be your responsibility to break. Whether or not that is worth it in the current horse economy when there are so many horses available right now.... I question it.
When they are circling him, he appears to have a nice gallop (would be nicer if they took off that wretched tie down!!! This is a perfect example of someone who is using a tie down INCORRECTLY.).
On the pattern, first barrel was *okay*. Second barrel was atrocious rider error. Hands up in the air, pulls him around, no collection, etc. Third barrel was about the same as the second, but worse in that he ended the turn much too tight for a young horse. He's going to tip them on the backside the way he have him patterned there. Young horses need extra room when they are starting out.
Second barrel run was worse ... not the horse, but the rider!!! Arm way up and out in the air on all the turns gives no support to the horse at all. However, really, the horse seems to be compensating quite well on the rider's part, so points for the horse there.
Yes these training things can be fixed ..... but do you want to try to break bad habits created by others? Sometimes it takes more work than it appears it would, so you need to consider that. This horse also needs a lot of work for training him to get down on his hind end for the turns which appears to be more of a training error, rather than the horse's inability to do so (with an improperly fitted tie down and poor riding).
I agree that there is NOT good conformation shots. Everything is off-set. Even the butt shot they cut the photo off at the hocks so you can't even see how his pasterns and feet sit. But you've got to look at him in person now, at least.
As far as his pedigree goes, he's got some speed in there. However, as I kind of said in your other post, if you are truly serious about getting a prospect that can be at the top of any large competition, you will need to spend some money to get some top bloodlines that increase your chances of getting that fast of a a horse.
That's not to say this horse won't be a 1D horse. You can never know that until the horse is finished. He may have the potential, but then again he may never be more than a 2D horse. You just don't know.
Based on the photo you took, and based on confirmation only, I would choose this horse over the other horse you posted because this one looks more structurally correct to handle the rigors of barrel racing.
And for your question on whether to sell you mare .... yes you may be attached to her, but if you are not happy with how fast she is, you owe it to her to sell her to someone that will appreciate how fast she is and meets their goals. So if you cannot afford to keep her AND purchase a prospect, then it's an easy decision to sell your mare simply because she will not get you to the level you want to achieve.