Pros: Parts for the 710z (as well as the 5500ss) are easy to get.
Cons: Both reels are out of production. They can still be found on the Internet.
Since nobody has written a review of the 710z, I thought I would, using the Penn 5500ss as a comparison, since both are made by Penn, and both are approximately the same size (the 710z being the older model).
Quality/Dependability/Durability: 710z. Aluminum housing, rotor cup & spool (5500ss has a graphite housing and aluminum spool). Thicker steel mainshaft. Brass and steel gears (5500ss has a thinner steel mainshaft and aluminum gears.)
Style/beauty: 710z (my opinion). It has the spool in the rotor cup design (the 5500ss has the skirted spool design).
Line capacity: 5500ss. Holds 325/10, 275/12, 225/15 (710z holds 300/10, 250/12, 200/15).
Light weight: 5500ss is 15 ounces. (710z is 16 3/8 ounces.)
Spools diameter: 5500ss is 2 5/32, while 710z is 2 9/64. Diameter is barely distinguishable when the spools are held face-to-face. The 5500ss has a slightly elongated spool, while the 710z does not.
Smoothness: 5500ss. Hands down. Also, the 5500ss is silent, while the 710z clicks during retrieve.
Retrieve: 5500ss. Rotor turns 4.6 times to 1 handle rotation, while the 710z only turns 3.6 times. With both spools full, the 5500ss retrieves 29 inches of line per handle rotation, while the 710z only retrieves 26 inches of line.
Line roller: 5500ss has a larger line roller. (Line twists haven't been a problem for me on the 710z even with its smaller roller.)
Drag system: Except for the drag knob, they both have the same internal drag system.
Line clip: Nope. You need a rubber band for both spools.
Casting ease and distance: 5500ss -- only by inches. Line binding to the spool has never been a problem for me with either reel. You can manually flip the bail on the 5500ss, while the 710z is locked open until you crank the handle. Sometimes the bail will flip without warning during a hard cast with the 5500ss, while this never happens with the 710z.
Which can handle more and bigger fish, and which will outlast the other: 710z. No contest.
Which is easier to work on: 710z. A simple design. If you're at all mechanically inclined you can service it yourself -- no need to send it in. (Of course this would probably violate the warranty.)
Overall ease of use: 5500ss. You take the little things for granted like the smoothness, lightness, quietness, faster retrieve, and being able to manually flip the bail, until you start using the 710z again. In fairness, you take the durability of the 710z for granted until you use the 5500ss again. If you're fishing around rocks, and drop the 710z, big deal. If you drop the 5500ss it could be a big deal (it's not metal like the 710z).