Here is a video of a creepy looking dude demonstrating how compression fittings work.
Compression Fittings and how to use them - YouTube
EK stuff is actually really good quality. Unfortunately their current designs have circles all over the place, but they are now moving away from that. Back in 2011 they had some issues with the nickle plating on their blocks, but they were really good about RMAing any defective blocks.
EK Official Statement for Nickel Plating Issues | EKWaterBlocks
Here is a video comparing 3/8 and 1/2" tubing from Dazmode.
How to select tubing for your watercooling setup? Review and tutorial. - YouTube
No difference between the "brands" of pumps. Usually it's just a different sticker. Yeah, they are all pretty plain, but there are other "tops" or reservoirs that integrate the pumps.
D5 Dual Bay Reservoir/Pump Combo | XSPC Bitspower 80mm Water Tank Z-Multi 803GP - Dual G1/4" Model (POM Version) Products Model: BP-WTZM-803GP-BK [BP-WTZM-803GP-BK] : Performance-PCs.com, ... sleeve it and they will come Bitspower D5 / MCP655 Mod Kit - Red Finish Products Model: BP-D5MA-RD [BP-D5MA-RD] : Performance-PCs.com, ... sleeve it and they will come
A reservoir is a reservoir. Just a place to store some extra fluid. If you plan on using a reservoir that integrates a pump, make sure they are compatible. Otherwise, just go for looks. A few examples:
https://frozenqshop.com/index.php/pr.../novacore.html https://frozenqshop.com/index.php/rcx160.html https://frozenqshop.com/index.php/bayres.html FrozenQ PC Mods Blue Meteor Light Limited Edition Reservoir - Blue Warp Drive Products Model: FQPC-WARPDRIVE-BL [FQPC-WARPDRIVE-BL] : Performance-PCs.com, ... sleeve it and they will come Alphacool - CPU Kühlung und Wasserkühlung sowie PC-Cooling und Silent-PC Artikel von Alphacool - Alphacool Repack-cooling Slot-In Black 15609 EK-BAY SPIN Reservoir - Plexi CSQ - Reservoirs - Reservoirs & Accessories EK-RES X3 150 - Reservoirs - Reservoirs & Accessories
Again, make sure your card and block are compatible. Not every 680 block and 680 card are the same. The block I linked is frosted acrylic, here is a pic from EKs website.