[MBAtarga]

I own a Mantis 2 stroke - and two other larger tillers.
As others have stated, the Mantis is great for already prepped beds to mix in more compost, etc. but all it's going to do with red clay is scratch the surface (literally!) I use it occasionally when I've dug a hole and am mixing in compost or mulch when planting trees or shrubs.
I use my Husqvarna 6 HP rear tine for the real work - tilling my 2400 sq ft garden annually. You will probably need to rent/buy something along that size for such a size plot (300 sq ft.)