East Coast Pro is an excellent showcase! Any player that has the chance to go should take advantage of it.
My son got his invitation after being seen by a scout at the Tennessee Baseball Coaches Assoc. showcase held at MTSU in June. The TBCA showcase has turned into an annual event and I felt it was very well run. I'm sure Bob is right that if you can be seen at a pro try-out this spring you can increase your chances of an invite.
As for East Coast Pro:
Held at UNC Wilmington in Wilmington, NC- great baseball facility, beautiful city, lots of history.
Chance for players to be instructed, and seen, by pro scouts. If they choose, can also stay in the dorms with the scouts.
Only around 130-140 players last year. Tremendous competition.
Easily over 350 college coaches and pro scouts in attendance.
As Bob stated, no fee to attend. MLB puts it on and the only cost was getting there, food and lodging. And of course that included same for parents!
One last point. Just being seen isn't enough to get an invitation. As with everything, you must perform when you have the chance. The total number of players from Tennessee there last summer was 6, I believe.
Good luck!