Swimming Fins

Fins are a great tool to use when doing certain drills in the pool when kicking would be too taxing and take away from the point of the dril (e.g., 1-armed laps). I only use them in drills because I'm paranoid of becoming too dependant on them (my kickin sucks) I've never used them in the open water 

I have aquaspheres and love them.  I also heard good  things about zoomers.

Hope this helps

You'll likely get 2 different opinions on this.  Many swim team coaches will say that fins are important for building leg strength and learning what if feels like to swim fast.  Others will say that fins should be reserved mostly for helping you to focus on technique while doing drills.  I'm of the latter school of thought...although I'm certainly not a swim coach or even a great swimmer for that matter.  There are several basic drills that focus on balance and body position which are difficult to master if you can't easily maintain some forward momentum.  Most triathletes typically have very weak kicks and some even move backwards when they kick on their back.  This makes focusing on proper body position and stroke technique in more advanced drills very difficult because you'll be too focused on kicking to keep moving.  A set of small fins is helpful in this situation because you can kick more gently and concentrate much more on the actual point of the drill rather than simply maintaining forward momentum.  As for using fins to learn what it feels like to swim faster...I agree but likely for a different reason from most.  Efficiency and streamlining is the most important aspect of swimming well...reduce your resistance and you'll move through the water easier and with less energy.  Kicking with fins while swimming whole stroke can create more speed and magnify inefficiencies in your streamlining.  Moving through the water fast will let you feel the water push against your body and allow you to recognize how your technique and position might be causing unnecessary resistance....especially in your head and hand/arm position.

So yes, get some fins, use them to help you focus on your drills and improve your streamlining/efficiency but don't worry about building your kicking strength...most swimmers generate very little propulsion with their kick.  The kick is mostly used for helping to initiate body rotation and counterbalancing that rotation.  Power comes from an efficient stroke and good streamlining.