the arduino scopes as pointed out are very slow in sampling, your old 70's scope is probably better
course yea you could go out and spend a couple car payments on a new slick lcd do everything model, I would love to myself
I have a 1987 model and while it is only 20mhz it is very useful and it has digital storage modes, so you can snapshot a live signals, zoom, and scroll while zoomed, along with OSD measurements such as a times voltages and frequency, and that was free
you can probably pick up a 90's model in decent shape for less than 100 bucks with similar features and higher speeds