Dan, glad to hear you're happy with your splitter. I'd like to add my 2 cents.
I have one of the 4 (or 5) ton units sold by Home Depot. It is labeled Homelite, but it is actually a rebranded Ryobi. From what I have been able to gather, Ryobi is the actual manufacturer of nearly all of these small electric splitters. Close examination of the details of the cylinder, pull-rod linkage, moving head and motor reveal them all to be the same. The Mantis also has exactly the same cylinder, linkage, etc, but must have a different hydraulic configuration to allow vertical operation. Even the 7 ton units have all the same details, so I assume there must be a difference in the pump to produce the higher tonnage.
I have had my unit for 3 years and I still love it. I share it with a friend, we both heat exclusively with wood in the mountains of northern California where temps can dip below zero from time to time. We each burn about 5 cords per year, so the splitter has been processing 10 cords per year. The only problem with the machine was related to forgetting to open the bleeder screw, which caused the seals in the cylinder to fail. It came with a 3 year warranty, so we took it back to Home Depot. They exchanged it on the spot with no questions.
The wood we split is mostly softwood (Douglas fir, lodgepole pine, western cedar and juniper), but we also get some Black Oak (Quercus kelloggii). The oak can be tough, the doug fir stringy and the juniper knotty. I cut my wood 17 inches long and this little splitter handles 95% or better with occasional need to reposition because of knots. I have stalled it in very wet white fir, the wood was so soft that the wedge was fully buried but the log wouldn't pop. In general we are working with 10 to 24 in. diameter rounds, but I have split oak rounds as large as 28 in. with no preparation. Larger rounds required a cut made by plunging the end of the chainsaw bar into the wood, then starting the split in the cut. Like Dan, I can't handle rounds much larger, so this limitation is irrelevant.
Because my back doesn't like working bent over, I modified the two-handed controls with foot pedals. This allows me to work standing up and frees my hands to control the splits. As for the safety considerations, my arms aren't long enough to get my hands in harms way when standing up. 8v}
Regarding the power cord discussions, I use a 12 ga. 75 ft cord. Remember that the motor does not run continuously unless modified with a toggle switch, so the power requirements are reduced.
Things I love about this splitter:
1. Effectiveness, it handles all my needs
2. Price, $300
3. Economy of operation, electricity is much cheaper than gas
4. Low maintenance, a little hydraulic oil from time to time and maybe some grease on the beam
5. Easy starting, plug it in and step on the pedals
6. Very quiet, I can hold a conversation while splitting
7. No fumes
8. Compact size and low weight, takes up very little space in my garage and I can pick it up and put it in my little Honda Civic wagon without help
I would recommend this splitter to anyone unless:
1. They are splitting large or tough wood
2. They are splitting commercial quantities
3. Electricity is not readily available
I hope this is helpful to others shopping for a splitter.
Craig