It would be great if Garmin Connect would allow manual input for body fat. My caliper is a pretty good one and I don't see why I should track this kind of data elsewhere.
I would not like to create .csv file every time I want to add my weight, body fat % etc. It is not user-friendly.
Well, that was a direct answer to the question. If you want it user friendly, buy you the Garmin Index scale, which will transfer the data to the GC account automatically and wirelessly each time you weight you.
Otherwise, you do not need to create a CSV file every time you want to import the data. You create it once, keep it on the desktop, edit it when needed, and then you simply drop the file onto the GC import page. It is almost as easy, and as quick as having to enter the data into some web form, so not much hassle at all. Or you can do it only once a week, or once a month (adding a line for each day), if you prefer.
You can also check whether the manufacturer of your weight offers an interface to Garmin, or a tool for exporting the data in some way that could be transmitted to GC with a 3rd party tool. There are similar solutions for some brands of weights, and you will find them here on the forum. However, often it won't be necessarily more user-friendly than the previously suggested file import. Using the Garmin Index is the easieast, and the most user-friendly way.
