Chances are the pull buoys at your pool look a little ragged, perhaps a bit closer to brown than white, with what looks suspiciously like bite marks. However, I would encourage you from time to time to see the pull buoy as an option to get in a great swim when you might otherwise have taken the day off.
Where I find the pull buoy most beneficial is when I get up in the morning to swim and my legs are concrete because I went too hard at the bike or run the day before. Perhaps it was a long run after taking a week off, or I got carried away at the velodrome with a fast group of riders. Either way, where you get up and would otherwise be too stiff to swim, head out and get a full workout without using your legs.
Triathlete.com highlights the pull buoy as a to enhance form, and I agree with this as well. In particular, I find that removing the legs from the equation allows me to really isolate body rotation and hand entry. Secondly, as an adult learner who has only recently gone to bilateral breathing, the pull buoy has allowed me to work on my ‘bad’ side. Try adding some one arm drills to perfect your catch, or swim looking at your hand entry, as you don’t have to worry about sinking. I would warn you though, if this is going to be a regular use, to still focus on keeping the hips up and not get lazy on form just because the floating is done for you.
Two major downsides to pull buoys are risk of injury and impact on stroke rate. Because all the power is coming from your arms, for those experiencing shoulder or neck pain, be particularly conscious of any increased tenderness. In regards to stroke rate, Ironman.com notes that improved buoyancy often leads to decreased stroke rate. I can attest to this, and the need to consciously keep a quick turn-over.
So, no excuses from heavy legs, use the pull buoy to get a great swim in no matter what. And if they sketchy ones at the pool put you off, you can get one for cheap at Amazon.