I can share my experience with an RK55HC.
I was drawn to the value and what seemed like a good tractor and solid service. I had seen this tractor sitting in the lot for quite some time, almost a year. I asked if I could have the newer model. Nope, they said. Then we spoke to the local mechanic. He was very responsive and helpful. So, we decided to buy it and a rake, box blade, and bush hog.
As first time tractor owners, the review of the tractor was fairly brief. I wished it had been more thorough. I did try to ask about every knob, button, and lever. Some questions the salesman did not know, and the mechanic was busy. I figured I would read the owner's manual. However, the owner's manual leaves much to be desired.
Two months in and only a box blading, raking, and some joy riding under our belt, with just over 8-hours, while going in reverse, smoke started pouring into the cab. Panicked, I shut it off, not knowing if I had done something wrong. The next day, I tried starting it. Again, smoke poured in. It was a weekend. On Monday, I reached the store mechanic. He told me to leave it sitting on the side of my drive and to not start it. He put in a request to the mobile mechanic. The mobile mechanic came in a few days. He seemed very knowledgeable and helpful. He found the hydro controller behind the dash must've had a bad solder or other failure, which started melting the plastic box. It wasn't anything to do with me luckily. No problem, he will just go back and get a new controller, return and I'll be in business. But... that particular controller was not in stock. The controllers for the newer models did not work. He'd have to order it, and it would have to come from Korea. Long story-short, a month later, still no controller. Supply chain issues. After much complaining and waiting for a new one to be assembled in Ohio, I finally got RK to take my dead tractor and deliver to me a new one. This didn't leave a good taste in my mouth. But I had a newer tractor.
The mobile mechanic looked at my bush hog and identified that the bleeder cap had been painted closed and not broken open. He said this could have blown the gears. He broke it open. Check that that cap on the gear box is free to move.
We lost a lift pin on our first bush hog session because I found the assemblers put the lock washers on the opposite side from the nuts. Only one fell off, but it bent some stuff and I had to buy a new pin. I didn't realize I would need to check their assembly. I believe implement assembly happens at the local store. So I suggest looking for some of these anomalies on the parts sitting in the parking lot.
I later found that the gear box had been completely filled with gear oil, instead of just up to the fill bolt. The oil was really foamy and poured out of the gear box. Check that they filled the gear oil properly.
Three months later, I planned on renting a seed drill. I called the local mechanic to ask a question about the rear hydraulic remotes. The local mechanic had quit. The store had no replacement mechanic. I called the mobile mechanic. He too had quit. Supposedly the store now has a new mechanic, but I have yet to meet him. He is always missing when I go to the store.
One month later, my A/C is blowing hot. The prior tractor salesman is now the store manager. He told me to just put a can of refrigerant into it. I know enough to know I could seriously damage the system by doing that. I could not get the mechanic to call me back. They had a visiting mobile mechanic who also did not call me back. I emailed and called RK tractors corporate and complained. They only had the local tractor salesman call me back. I did talk to the new tractor salesman. He said I could not have a visit from the mobile mechanic, because the tractor was not "dead in the field." We decided that I will have them correct that under warranty when I bring it in for the 50-hour service this next year.
Lastly, I found several large frame bolts loose on the tractor under the engine and cab. I do not know if this is normal, or if it was an assembly problem.
I currently do not regret buying it, but it has been an ordeal to say the least. I am not sure if another tractor would have experienced the same issues. I have been disappointed with the mechanics quitting. I still think it is a good value for a new tractor. I am thinking that the melting, smoking controller was a fluke.
Let me know what you think and what you decide.