First, a little background to let you know "where I'm coming from". I used to snorkel with Cressi full-foot fins in the 1970s. Back then, Cressi set the standard by which everybody else's full-foot fins could be judged. After all, Cressi invented the full-foot fin design. I was very happy with my Cressi Rondines, which I used when snorkelling in the Mediterranean. I don't snorkel with Cressi fins nowadays because after the 1970s, like many fin manufacturers of the time, they jumped on to the thermoplastic footpocket cum plastic blade bandwagon. They lost my custom because they no longer made the all-rubber fins that made my snorkelling a pleasure.
This said, there's really no point in asking somebody else whether a given brand of fins is going to suit you and what you want to do with them. The first criterion with fins is how well the foot pockets accommodate your feet, which doesn't just mean lengthwise, but also width- and height-wise. Another ScubaBoard thread suggests that there may be a problem with the Pluma's foot pockets. Judge for yourself by reading the thread at
http://www.scubaboard.com/forums/cressi/286406-cressi-pluma-fins-extremely-poor-design-render-them-useless.html
If nothing else, such exchanges flag up the need to apply critical judgement when selecting and purchasing fins.
You mention that you may want to use the fins for scuba as well as snorkelling. The conventional wisdom here on SB, mostly professed by wearers of open-heel fins, is that full-foot fins can only be worn barefoot and that open-heels, which can be worn over boots, are therefore the only option for scuba diving. This is only partly true. Full-foot fins can be worn over socks or thin booties, but you have to buy a pair a size or two bigger than your normal shoe size to accommodate the extra bulk. Back in the 1960s, when I did some dive training here in the UK, divers often had two pairs of full-foots, one normal-sized for the pool, the other one or two sizes larger for open water.
So, to come back to your Plumas, they certainly wouldn't be my choice, because I don't snorkel with tupperware. However, they may be just what
you want and need. If you're in doubt, try and borrow as many pairs of fins as you can and try them out one by one to see how each one matches your criteria for comfort and efficiency. Remember that fins are worn for power, manoeuvrability and endurance, not speed, and no single fin fulfils these criteria in equal measure, no matter what the manufacturers and retailers say. Finding the best fin for you, not anybody else, is a personal odyssey, nobody can make the decision for you, so be wary if anybody else recommends a particular brand. The brand may work for them, which doesn't mean it'll work for you. We're all different.