I bought the RBK 5K's last October. I use them about four times a week, so that's about 70 games. Still holding up well, though they're getting pretty dirty because I don't believe in washing off puckmarks. They show character.
The 5K's don't break in well. They still won't hold an S-shape for me after all this time. The foam is just too hard. The 7K's also have this problem, but the P1's, P2's, and Premier Pros are better at this. They're also made in China, which may be why they're cheaper.
Durability can be an issue. My pads have held up well, but I've heard horror stories from others. My knee lifts are becoming frayed, the stitching is fraying, and the holes in the (synthetic) leather are slowly being stretched from the threading holding the foam in place. On the plus side, things like the straps are holding up well.
The calf and knee guards are also synthetic leather (Jenpro, IIRC), which makes for easier sliding. It's not Clarino, but it's a lot better for sliding. The pads are also very light compared to my previous set, so if you're used to traditional, stuffed pads, these will feel like there's nothing's on your legs.
Most, if not all, pro-fly pads have toe-ties and knee lifts (gives extra height under your knee in the butterfly position). IMO, these two features are essential for people learning the style. Knee lifts make it a lot easier for you to flare out your legs. Toe-ties give the option of having slack between your toe and the pad's toe...so your feet can angle downward, taking pressure off your ankle, instead of being parallel to the ice.
Toe-ties can be a problem depending on your skates. If you still have skates with older, metal blade holders, then they'll eat through the toe-tie laces and you'll have to replace them after six or seven games. If your blade holder is made of plastic, you'll have no problems.
The thigh guards are awesome for helping to block the 5-hole, but may be illegal in some leagues (they're not NHL-legal). I used to wear separate knee/thigh guards, but haven't with these pads. I've only been hit in the knee twice, both in close quarters with soft shots.
So...the 5K's are a good beginner pad, though they'll probably have to be replaced after about two seasons, depending on how often you play. Not sure how they'd play if you're a stand-up goalie, however. They could be a bit bulky.
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