Totally right. I'm a reluctant Mesa owner (will drop him for a set-up guy or someone who takes over for an injury if I can) but looking at his past 3 years, there's a chance he could perform really well. Have a look:
2001: 2.34 ERA, 1.23 WHIP, 0.85 K/IP, 2.95 K/BB, 3-3, 42 saves
2002: 2.97 ERA, 1.37 WHIP, 0.85 K/IP, 1.64 K/BB, 4-6, 45 saves
2003: 6.52 ERA, 1.76 WHIP, 0.78 K/IP, 1.45 K/BB, 5-7, 24 saves
So numbers like a 3.50 ERA, 1.50 WHIP, .8 K/IP and 30 saves are not unrealistic. The WHIP trend and the K/BB trend is something to be concerned about, but if he can rebound, there is an upside of 40 saves with a decent ERA.
He's worth the risk, but nobody to bank on.