I use wafer extensions out of necessity — my wafer tape border tends to pull away from the top no matter which brand I tried (Coloplast, ConvaTec, Hollister). They do add an extra level of security. There are at least two reasons you can have soreness in the area of the barrier extension:
1) Are you pulling on your skin when you remove the extensions? If so, you may need to use an adhesive removal spray/wipe. Are you removing your wafer too frequently? If you are removing your wafer every 1-2 days, the skin can get very irritated with such frequent changes. Are you keeping your wafer on too long? If you are keeping the wafer on for more than 4-5 days, the extensions tend to break down and leave more adhesive to clean up. I find Hollister extensions adhere very well but can be difficult to remove. Try multiple products to find the one that has the best trade-off between adherence and ease of removal. Remember, when removing the barrier extension, to press down on your skin, not pull up on the extension.
2) You may be allergic to the adhesive used by the extension. Try different extensions such as: Coloplast's Brava Elastic Barrier Strips, Hollister's Adapt CeraPlus Barrier Extenders, ConvaTec's Ease Strips, and Entrust's Crescent Barrier Extension.
You should at least see if you even need an extension — if you can get 4-5 days wear time without an extension, then there is no need unless you are going swimming. You can also add a level of protection by wearing a belt/wrap/ostomy vest/etc.