Those lathes and mills are so small, and light, that they are borderline worthless. You wouldn't think you'd need anything larger for bike work but you do, and once you get them you'll find many other uses for it, and that's when the size will be limiting.
Even mitering tubes will require something with a bit more beef. Holesaws chatter some and that will really test this small machinery. The carriage and crossfeed are simply too small/light to hold an adequate fixture for holding tubes. Weight is your friend.
I have an old ('40s) Southbend 9 inch and it's borderline too small. The spindle bore is 1" and larger would be much better. The swing is too little. The length is too short. Though it's a great lathe and in excellent condition, it's just too small. Even at 400# it's borderline light. It was easy to get in the basement though. It is basically three pieces (minus the motor and clutch). Remove head and tailstock from bed and carry each individually.
Also, I don't use this lathes for mitering tubes. I built five frames last year and don't anticipate any more than this, so tooling up for this doesn't make sense. I've coped some joints using a boring bar, and it's slow going. I know guys get by with using holesaws in a lathe, but I don't think mine will handle it comfortably. Using a cutter like Andy Newland sells (Lan-71) would work great, but the cost is out of range for a few frames a year.
To give you an idea of costs, I paid $1600 for this lathe. It was a steal considering the condition and tooling. I can sell the whole mess and probably even make a little money. To keep the wife happy buy something you can actually use that will hold it's value.