I texted the company asking for "tips" on installation. They were less than helpful...saying they do not have an install guide (didn't ask for one...just wanted helpful tips) and said "...cleaning the surface and then installing the product will suffice for install." Okay... thaaaaanks. So, I thought I'd share what I ended up doing for what it's worth.
I bought extra tape -- "Double Sided Tape Heavy Duty, 3M 5952 VHB Mounting Adhesive Tape 1/4 in x 15.4 ft, Waterproof Adhesive Strips Tape for Indoor & Outdoor, Automotive Trim" -- on Amazon and added 2-3 strips off added tape wherever I could on the inside of the covers. I taped up one handle before applying it to the car practiced "putting it on the car handle" with an un-taped handle cover first...figuring out the best way to put the cover on once the tape is peeled back...assuming you have "one shot." For me it was putting the "pointy" corner of the handle in position first and then laying the handle in place from there. The hardest part of the ENTIRE process (for me) was peeling the damn protective layer of the tape off to get to the sticky surface....I ended up working with a magnifying glass and tweezers.
I cleaned my car handles really well with cleaning solution, followed by alcohol, followed by ample air dry. I then took my handle covers loaded with extra tape and one-by-one heated the taped side with a hair dryer till the tape glistened. Once one was heated I applied it to the car handle and used my hand to apply pressure for a couple of minutes.
I really am pleased with how they look. I'm so mad that I didn't take pictures before applying the covers... My original handles were a chrome color and the part of the handle where your palm goes didn't age well with the car and was terribly cracked, peeled, and a total "eye sore" all along the seams -- I hated how it looked...which gave me the courage to try these covers.
I'll let you know if they don't stay on...but they sure seem to really be on there! Oh, and my 4 Runner is a 2012 Special Edition and I don't mind at all that the covers aren't flush with the handle seam (they warn you of that). It might be because my car is silver...not sure. I tried to get pictures of it to show what I mean.
Good luck! Do it!