The Johnson blues harps you're looking at aren't terrible, but they are a pretty low quality play, in my humble opinion. I had one for my first harp and tried to pull it back out recently but realized it's a pretty leaky harp and doesn't handle well.
If you've been dabbling for 4 or 5 years, my advice would be to buy one harmonica that you've never played before in a key you don't often play (or never have). Spend anywhere from $50 to $100. And then just keep doing that every so often. It will change your style and give you a wicked collection of musical personalities.
Go spend $50 on a Suzuki Promaster if you've never played with one. The metal comb isn't as warm and rich as a wood comb, but it's airtight and handles like a Japanese sports car. Great volume control and tight bend control. It's a great harp that I find a lot of players aren't familiar with. I love 'em.
If you want to get crazy, go spend $65 on a Suzuki Firebreath. It has a wooden comb for a warm sound but still bends and handles like a Japanese sports car... albeit a wooden one. A thing of beauty, really.
Golden Melodies are great harps for the price. They're the only plastic comb harp that I truly enjoy playing. I have Special 20's, Suzuki Bluesmasters, and Lee Oskars but I think the GM has a much nicer sound and warmer tuning. Handles nice. Good volume. Great for straight harp playing. (If you don't play a lot of straight harp already, I recommend one of these. It will make you want to play in straight harp and your style will adapt to it. Did for me, anyway.)
Ooh, and my most recent discovery is the natural minor and harmonica minor harps. Lee Oskar's aren't the best harps, but the alternate tuning makes you (eventually) play wicked new songs! You just play things you already know, even, but because the tuning is different, you find new music! Try one, they're pretty fantastic. I don't see it on Amazon, but I recommend finding the harmonica minor.
TL;DR - Spend $50 - $100 on a single harmonica in a type you haven't played before and in a key you don't play often. Play. Repeat.