4cm Nerf Rail
I really don't know what to say about the 4cm Nerf rails. They work, and work well. For $3 AUD + $1 AUD postage per rail, it's much cheaper than getting a blaster to slice a rail off.
Nerf Rail Blank
The Rail Blank can be attached to almost anything, provided it can be suitably attached. Epoxy is the recommended method, but a combination of hot glue and screws also works well.
There's not much else to say about the Rail Blank either. If you're looking for a way to attach custom made accessories and want them secure, the Rail Blank is the way to go. At $4 AUD + $1 AUD postage, the Rail Blank is cheaper than buying a Recon to cull for the attachment pieces, and much more stable than any attachment Nerf has made.
Nerf Rail to Rail Connector
Like the other pieces, there's not much to say about the Rail to Rail Connector either. It does its job properly, holding to rails together securely and easily. It allows for some easy psuedo-integrations, ideal for when you're not sure whether to complete an integration of not. It's also fun to tool around with on all sorts of blasters, like attaching a Stryfe to an Elite Alpha.
In summary, a bunch of simple and effective rail related Slydev attachments. If you're looking for rail-related tacticool, Slydev is the place to go.