Stihl Combi or Trimmer Plus are both good products. The Trimmer Plus attachments will work on the Stihl head. My son has the much more expensive Stihl Combi, but we've used my hedge trimmer, mini-tiller, and pole saw on it. He gave me a few trimmer heads for the Echo system that he thought he could no longer use, which turned out to be a boon for him when he accidentally backed over his brand new trimmer head for his Stihl. Still haven't figured out how that happened, but I have my suspicions. The Echo and Trimmer Plus are virtually identical in the connection, but there does seem to be a slight advantage in the Troy-Bilt brand quality. But, obviously, the higher the quality, the higher the price. But you didn't ask about something you may not have or want. You asked about a manual pole saw.
As for your manual pole saw / pruner, put some grease on the pruning blade pivot on occasion. If you still have the cheap plastic rope on it, go get some 3/8 nylon starter cord, about twice the size of what you find on anything with a recoil starter. It doesn't stretch. Paracord works OK, too, but is smaller and will wear a little faster. You might find some larger paracord if you look long enough. Some of these tools come improperly laced from the factory so that you don't get the compound pull. The end of the cord should be tied to the blade, threaded through the roller at the base of the head, then back through the roller on the end of the blade lever. That doubles the pulling force. The blade will probably take it, but your fingers may not. I've seen many with the rope tied around the roller on the base of the head. There are two rollers for a reason. Keep a piece of 4-inch 3/4 diameter dowel pin with a notch cut around it in your pocket when using the pruning shear. This is not to impress the ladies. A quick clove hitch around the dowel will save your fingers and wrist from some pretty wicked forces that are NOT good for carpal tunnel syndrome or arthritic fingers. Don't snatch. If you're snatching, you're using the wrong tool. Use the saw. Let the weight of the saw do most of the work. The blade is curved for more than one reason. They become very apparent the more you use it. The farther from the trunk you get and the smaller the limb, the less useful the saw is. If the limb is still too big to cut with the pruning shear, you're going to have to find an alternative (see opening paragraph).
A polesaw/pruner is like any other cutting tool. It has to be kept sharp. This isn't really difficult if you hang it up when not using it. The shear is easily sharpened with a common file. A whetstone takes entirely too long for the task the blade is intended, but others may have more patience and less to do than I. I keep my pocketknife razor sharp with a Smith's sharpener system which I do while I'm sitting on the deck having a cool beer and cooling the jets after a day of yard work. Pruning shears get a quick rub with a file, reassembled, and re-tensioned, and put to work. If you protect the blade and don't twist when cutting, there's little danger of dulling it just cutting tree branches. About the only thing that can do that is the blade hitting the anvil or cutting dirty limbs on the ground. Monitor the pivot bolt for wear as that will let the shear wobble and possibly hit the anvil more often. My cheapo saw is at least 30 years old and still going on original blades. Some saps are corrosive (especially hardwoods) so clean them off and put some oil on them before storing them long term. A kerfing tool is not real expensive, and you can actually use a triangle file to sharpen the teeth on the saw rather than just replacing it. Some can't be bothered and just get a new blade. There's something strangely satisfying about seeing a blade I just sharpened slice through something.
