Bicycle power meters are without a doubt the most influential training technology to come down the pipeline in decades.  Once a mythical device used by the rich and pros that spouting such terms as "normalized power" and "variability index" the power meter is now accessible to the masses.  There are high quality power meters to be had near the $500 price point and they have become much more simple and easy to use.  They work over a variety of software platforms and across a myriad of devices including your smartphone.  Calibration and pairing that used to be a nightmare is now down automatically and seamlessly for the most part.  Best of all power meters have opened up a panorama of indoor training experiences and options to keep you occupied through the winter.

However, there can be some buyers remorse.  By asking a few key pre-purchase questions you may head this off at the pass.  These will ensure you not only buy the right power meter for your bike but the one that has the features you need- or don't.

1.  What is my price point?  Start off by asking yourself what is your price point within, say $100.  This in and of itself with narrow down your purchase options.  Power meters can be very confusing, especially when it comes to compatibility with your bicycle.  By setting a price point you will likely eliminate some brands and models making the purchase decision easier to begin with.  As you can imagine the cheapest power meter is not going to be the best.  Some power meters are not true power meters in that they do not measure strain or torque and convert this into wattage.  They attempt to infer power based on a variety of environmental factors.  I recommend buying a strain gauged based power meter.  

2.  How much technology do I need?  As you move up in price point you get more advanced features and analysis like left/right power, more strain gauges to measure your pedal stroke, and presumably more accuracy.  But if you are a cyclist that does not upload ride data, or does not want to, then you do not need to pay for these features.  I find many cyclists are happy to monitor their average or normalized power, personal bests, and to compare rides in a simple format.  A power meter that sends the Bluetooth signal means you can use a variety of apps and software platforms on your smart phone or tablet.  If you want to try apps like Zwift or Trainer Road this is a must have.     

3.  How many bikes do I want to measure my power on?  Some cyclist only have budget for one power meter yet the have a road, time trial or tri bike, and/or other.  Portability between bikes may be high on the list.  Unless you have exactly the same crank, in exactly the same length, across your bikes, you may want to rule out a crank based system and go with a wheel or pedal based system.  Pedal based systems are best for portability in that it is easy to remove your pedals and most cyclist run the same pedal system.  A wheel based system is also highly portable but you are limited to one wheel choice.  Some cyclists will build a custom rear wheel with power meter hub to meet their specifications.

4.  Will it work on my bike?  Most brands of power meters attach to the crank in some fashion either at the crank arm, rings, or spider of the crankset.  This can be very confusing for the uninitiated.  You can buy the right crank with the wrong crank length, or the right crank with the wrong rings, or the right crank length with the wrong bottom bracket interface, the right brand but the wrong model, the right power meter but it has a clearance issue with your bicycle frame, etc..  First understand the you need specific information on your crank, not necessarily your bike.  Bike manufacturers may switch a crank model mid-production. If you have a Shimano or SRAM groupo don't assume you have a Shimano/SRAM crank; you may be running a different brand such as FSA.  This is fairly common.  You need to know exactly what brand/model/crank length you have in order to purchase the correct power meter.  Clearance issues, meaning the power meter contacts your frame, are a lot less common now that power meters have become smaller and thinner.  But you should check the power meter manufacturers website for known clearance or compatibility issues- most list clearance dimensions as well.

5.  How old is my bike/drivetrain?    I added this last question as it is an important value consideration.  If your bike is very old and you know that you are in the market for a new one soon, I don't necessarily recommend purchasing a crank based power meter.  The chances that your power meter will be compatible your new bike are relatively low; after all you don't even know what that crankset will be.  Pedal and wheel based systems are more forward compatible.  Even if you plan on running the same drivetrain, If your bike is a few years old the drivetrain may be a generation or two back.  Power meters are a technology like any other that becomes obsolete fairly quickly.  I also recommend checking your chain rings for excess wear.  If you are due to replace your rings or upgrade your crank you may want to buy a power meter that comes with new rings and kill two birds.  This will likely save you a bit of money.

Hopefully this will help you head off any issues at the pass and purchase the best power meter for your needs at the best price.  It most likely will not be the cheapest power meter but it will be the best for you.