Different brands have different connections for handles and bands. Some have the clip on the band, some have the clip on a removeable handle. Caribeaner clips are always an option if handles and bands both have rings on the end (this should not be an issue when using products from a single-brand kit, or product line, but most brands have different product lines with varying clip options). Heavy duty climbing clips are MUCH safer than the key chain clips. It is a matter of personal preference to have foam handles or rubberized handles. Sometimes the rubberized handles can be easier to clean. For ankle/wrist cuffs, Bodyastics has a very comfortable neoprene lined thick hook-and-loop strap.
Triceps extension ropes can be a quality add-on to any home gym set up. Larger bars for squats and dead lifts do not often come standard with exercise band kits.