Do I need an instrument to start…?
The main function of a variometer - to measure the change in air pressure to tell you when you are going up. On a soarable ridge that is more obvious than you might think, thermalling, on the other hand is a little harder and without any inherent spider sense requires as much help as you can get. Audible varios are a real useful tool.
Varios offer audio only so an up and down noise, very small and relatively cheap. They can also offer a visual display with memory that records your altitude and measures the length of your flight. Useful for keeping a log of your hours, and especially if you fly during thermic periods near congested or prohibitive airspace areas.
For instance, If you have a ceiling of a 2,000ft above your local site, flying without would be deemed reckless and potential airspace infringements are damaging to the sport, irresponsible and come with CAA fines and potential prosecution or flying over the back of the hill and landing in a no-flying zone.
Vario Gps: Integrated units are now the norm, so if you're planning to get stuck into thermal flying and Xc then best skip the visual vario and go for the full functionality, you’ll learn more about the instrument as and when you need it. Many instruments come future proofed for free software upgrades.
Basic Gps units offer ground speed which is essential for Xc pilots working out wind strength and direction. Many units now offer a last thermal function, so they track the last piece of lift you entered and fell out off and show you a mate where it is in relation to yourself. The more high-end units offer preloaded airspace maps, warnings, and now live tracking which is both useful fro safety and retracing your best days on google maps when the weather is lousy! Top end Gps are competition rated and allow the loading of predefines tasks route optimisation etc…
So Do you need one…If it’s not a budget decision then go for the integrated Gps, if you are off to the mountains, get some form of live track facility. If you only ever fly at coastal sites I wouldn’t bother and enjoy the peace and quiet. If you are on a budget then start with an Audible only device.