There are many solutions to the scenario you are facing. What you have done is really creative.
I have attached a report with two ways to implement a single horizontal bar on each detail row.
First of them is using a Chart reporting item. The chart contains only one series, with one item. This way the chart contains only one bar. The properties of the chart are setup so that it does not show labels, legend, etc. The good think about this approach is that the bar's look is fully customizable, you can set gradients, shadows, etc.
The second approach is based on your idea to resize an item according to the value you want do display. In the example is used TextBox item with background color. The good thing about it is that it is really simple. However, there is one hitch. The current release does not allow you to change the size of a Telerik.Reporting.Processing item (and that are the items you access in the OnDataBound events). The good news is that next week service pack will be released that will untie your hands. So you will only have to uncomment the row
'bar.Size = size
and it will be fully functional.
It is up to you to decide between customizability and simplicity.
I hope this information helps. Please do not hesitate to write us again if you have any further questions.
the Telerik team