I agree with almost everything Rex mentioned, especially the emphasis on cleaning. If using wire brush, grinder, sander, etc. it is usually best to use one dedicated to one type of material, i.e. aluminum, stainless, steel & its alloys, etc. Cross contamination can cause big problems, especially iron into aluminum.
The only point I disagree with Rex on is the final strength of a splice of the type in question. At best it will achieve a strength equal to a single tube with the OD of the outside tube and ID of the inside tube. This still puts it far above the strength of the parent tube.
Beveling of the tube ends is good practice when the tube wall is of a thickness that would warrant it. Thinwall tube such as .049, .065, etc. need no bevel, just a slight gap between the ends. Wall thickness on the order of .188, .250, and thicker will virtually always benefit from a nice bevel as Rex described.
Hint: When replacing a tube where splices are needed at both ends, the inner sleeves can be placed inside the repair section, then pieces of MIG wire attached to the sleeves and run out through holes in the parent tube past the repair area are used to pull the sleeves into position.