Insulators are of different types, like home insulation systems, cabling etc. Their testing and checking of insulation level is required before getting those in use. Therefore, insulation testers are needed to serve the purpose and help mankind. If the insulators pass the test, then they can be recommended for use.
Buying these devices at commercial levels is extensive because almost all businesses and corporate offices need these. Individuals too take interest in buying these because they require such devices at domestic level. Many companies claim that they manufacture the best insulation testers but popularity graph of brands can be checked before cracking a deal.