When you are looking for a vario there are certain obvious considerations like features, size, weight, warranty, battery life, etc. that will effect your decision, however there are quite a few other factors you should also consider.
Having a long laundry list of features is not nearly as important as having the right useful features. Some features are gadget features that have no real benefit for flight. When considering a vario ask yourself about each of the features and evaluate if they will really assist you in climbing faster, getting higher, arriving at goal faster or flying further. If you are a newer pilot you will find that these unnecessary features will be a distraction rather than a benefit. A good entry-level vario will provide information that will assist your flying without interfering.
Feature are useless if you do not understand them, or they are too difficult to program and/or utilize. Find out if the vario you are considering is user-friendly. The best way to do that is talk to fellow pilots, see what vario they are using and if it is a pleasure or a chore to use. A good flight instrument should provide the necessary information with little or no input from the pilot.
This is one of the most important considerations. There is a lot of good technology out there but what do you do when you need help using or understanding it? What do you do when you need a repair? Will you be able to call and email someone experienced and knowledgeable to get the help and answers that you need in a timely fashion or will the answer that you are looking for involve several unanswered emails, followed by several unanswered voicemails. Once you connect with someone will you get friendly knowledgeable answers or will you get a bunch of “maybe”, “I don’t know” and “I’ll get back to you”. Before you invest in a vario find out about the reputation of the local distributor.
This one is also very important. After all, what good is a vario when it is broken? Find out if the vario you are considering has local service or if it will have to be sent to some far off place for "you'll-get-it-when-you-get-it" service. Products that must be sent out of the country can take 6-10 weeks (or more) to come back from repair. Typically there is considerable shipping cost and increased risk of loss associated with overseas repair. This is an easy one to check - ask your local professional HG/PG school, dealer, flightpark or instructor about the service time on the product you are considering. Also check with your fellow pilots and find out what their experience has been with the vario that they use.
Many instrument manufactures, importers or distributors have changed hands, discontinued the product or worse gone out of business (some more than once). If any of these situations occur while you need service or support you will find that it will be very difficult to get the service that you need, or worse, it simply will not be available. Before you buy a vario do a quick check to see how long the manufacturer has been in business, how long has the distributor/importer been in business and check to see if they have orphaned varios and customers in the past. The continuity of the manufacturer and the distributor is very important to the resale value of the vario. The less stable the manufacture/distributor the worse the resale/trade-in value.
If you are buying a new (or used) vario make sure you are getting it from an authorized dealer. Products that do not come from authorized dealers are gray or black market. Usually they do not include instructions in your language and they will lack local warranty and local customer support. Buying these products also supports illegal and unethical business practices and is very damaging to our sport and in the long run causes the price of these products to go up. Authorized dealers are approved by the manufacturer/distributor and they provide valuable service and support to their customers.