Recently a friend was having problems getting sharp images using his 500 f/4 lens. All the images were soft at a distance of 75 yards and longer. He was using it on a Manfrotto alloy tripod with a Jobu Jr. gimbal head.
While testing, we had his kit set up side by side with my RRS carbon fiber tripod and RRS ballhead with a Wimberley Sidekick and a 200-400 lens. You could see the front of his lens visibly moving any time a truck drove by or someone walked on the nearby boardwalk while my kit did not move. I was able to film the difference with my iPhone and you could see it clearly. Even with good long lens technique and a hand firmly over the lens barrel, vibration was reduced by 2/3 but still visible. He replaced his gimbal head and used a better tripod a few days later and suddenly his images were sharp.
There is a saying about overspending - something along the lines of "Don't put a $100 saddle on a $50 horse". It would not make any sense to buy a $1500 tripod and gimbal for a $1000 long lens. But if you have a good camera and an expensive lens, spending a reasonable amount makes sense. If you already have a good ballhead, a Wimberley Sidekick is an option in place of a full gimbal head. If you don't have a carbon fiber tripod, it's a good idea to get a good tripod that supports a long lens.
The Promaster gimbal head is probably good enough for occasional use with a moderately priced, light, long lens like a 200-500 or 150-600 if you have good tripod legs already. Invest in a better gimbal head if you have a bigger lens, a higher cost lens, or you are going to use it frequently and are fussy about image quality.d to trouble-shoot even more…