There has always been much discussion on these retracts, as well as the CenturyJet rotating retracts, and at least 2 other limited production replacements (Sierra and RobinAire). I suggest anyone considering any of these choices do a search here at RCU, and you will discover many opinions. This has been hashed over thoroughly, so the answers are here if you learn to search.

I will take a few minutes to re-state my own opinions:

Robart 615s with RoboStruts:
+) The best looking of the bunch, with great scale appearance
+) RoboStruts do a great job of shock absorbing, especially if gear is installed with slightly forward angle when down.
+) Comparativley compact desgn fits in retract bay well very nicely, with no modification to wing spar needed.
-) Very weak "links", or scissors as some refer them as. These become bent way to easily, and are essentially useless once they become bent. Best thing to do is stock up on replacements (about $6 each) there are 2 on each retract, 4 total in set, so a really unforunate landing can cost about $24. As this post implies tho, I have discovered a modification which has greatly reduced the tendancy for these to become bent.
-) All those set screws can become a nightmare if not properly installed. I use 4 on each RoBoStrut, and grind a flat spot for each one, and no more problems. If you fail to grind the flat spot, you WILL have problems.

CenturyJet:
+) Robust desgn, is much less likely to become damaged (altho not impossible as I have seen).
+) Units are completely assembled with shock absorbing oleos, no set screws to mess with (or mess up).
-) Bulkier units require a hole to be made in main spar for cylinder clearance, less room for instlling gear doors.
-) Oleos look cheap, not nearly as nice as RoboStruts. Also seem a little stiff for the lighter (8 ~ 9 1/2 lb) aircraft.

Sierra:
I have never owned a set, but have 'fondled' a set, so here are my impressions:
+) they do appear to be very well built, and are probably sturdier than the Robarts
+) they have a nice appearance, but not as good at RoboStrut equipped Robarts
-) They look all wrong when retracting: all of the 'rotation' occurs during the 1st half of the retract cycle. Not only is this an appearnce issue, it can also create problems if you intend to install operating gear doors, as the struts need to 'tuck' into the bay at a slight angle, rather than go in straight and level.

RobinAire:
I have never seen these units, except in pictures and drawings.
+) Robust, or at least that is the claim
+) VERY nice looking, and the units allow the struts ti be VERY close to the wing leading edge, for the best scale location
-) Units are very bulky (large), meaning it will be difficuly to install in some of the other 1/8 scale Corsairs (such as Hanger 9). Mounting width is by far the widest of the lot.
-) Struts are very long. Altho this makes them more scale, I personnaly would trade off form for function here. Shorter struts make landings easier, and tip overs less likely. It also makes installing larger wheels more challenging, as the rear spar comes into play. Longer struts also have a greater influence on changing center of gravity (wheels go back farther).

As for cost comparisons: that is up to the individual. I have learned that building a scale warbird costs a lot of money by the time it is completed. I'm not rich, and don't like spending any more than I have to, but I do tend to buy what I think will work best. I don't want to skimp on the retracts after spending all the other time and money on such a project.

Just my 2 cents.