I'll confuse you some. Sorry.

I've owned 3 different tractors with removable backhoes. As others have said, they really are great for trenching, landscaping or working on a smaller stump. Problem; they are a PIA (IMHO) to remove and re-install when I need the to use the PTO for bush hogging, clearing snow with a snow blade or moving dirt with a box blade. I found that I generally left it off and tried to rent a backhoe for my 'real' backhoe work. Not really cost efficient.
So, when I sold my last tractor with a backhoe (and, no, it didn't help much at all on selling price or ease of selling - most wanted to know how much I would take for my tractor if I kept the backhoe

). I bought a larger tractor and a 10 year old 580 Case backhoe. If I could get my wife to help, she would run the tractor with a 1 yard bucket on the front and keep the dirt pretty much out of my way. However, I then found I really wasn't using the FEL on the backhoe.
I then made a mistake of renting a Takeuchi TB175 mini (really big for a mini, just over 17k pounds. Anyway, it absolutely positively ran circles around a backhoe when it came to really moving dirt or digging out larger stumps or rocks (boulders?). So, I sold the Case and bought me a Tak TB175 open station machine (since it's used in the woods a LOT). Being that it ran circles around a Case 580, it made the tractor add on backhoe seem like a toy for limited duties. Yeah, I liked the TB175 so much that I bought one with rubber tracks. The rented one with steel tracks was too hard on concrete or asphalt.
Right now the prices are going up rather quickly on mini-excavators as more and more contractors move to them as opposed to any backhoe because most contractors already have a skid steer or compact track loader (skid steer on tracks). I was fortunate enough to buy two Bobcat mini excavators, fix some small issues and have a friend paint them up to look new at his shop where they specialize in media blasting industrial equipment and painting them. I was able to make enough off the two Bobcats to almost pay for my Tak. So, being somewhat prudent, I sold off 1 backhoe I had to keep to sell one of my tractors on eBay, sold off other now not needed implements and bought a Tak TL150 to go with my excavator.
With zero turn radius mowers and other mowing equipment, my tractor now doesn't see that much use except in the spring when I put the 'non-loaded' R4 tires on it (making it as light as I reasonably can) and cut trails in on my property with my 8' rotary cutter. I have a wonderful Woods 990 I bought for it that just sits on the shelf and hardly ever gets used.
So, you can see that buying a backhoe attachment for my tractor cost me some money! It sure beats using a shovel for certain! However, when compared to my Tak TB175, it became no more than an expensive toy that I didn't enjoy taking on and off. So, my reply would be completely based on what you intend to do with the backhoe. For clearing 10 to 13 acres, I'd spend a fraction of what the hoe costs and just have someone else clear the property in a weekend for me. Then use your CK27 for clearing, leveling, tilling and other uses on your property. However, if you "just gotta have one" when it comes to a backhoe, buy one; either the add on for your CK20 or, for a few thousand more, a stand alone backhoe you can later sell. Your mileage may vary, but that's my experience.