I found the straight shaft trimmers are the best choice. Most models come with brush cutter attachments which can be used quite often in clearing up rough, small woody areas (natural areas).
You can also use them to edge flowerbeds and driveways. After a little practice you will be a pro. Edging and trimming is very important for the manicured look customers today are looking for. They are paying for a quality service and will expect an immaculate job. It makes a big difference in the appearance of a job.
Using the trimmer as an edger will save you money since you do not have to purchase a rolling type edger. I caution you to make sure you and/or your employees wear safety gear when edging or trimming. Trimmers are notorious for throwing objects at you such as rocks, glass, etc. Be sure to protect your eyes and wearing long pants. Furnish each employee with safety glasses and insist on wearing them.
The rolling edgers are a slow and tedious way of getting the job done. Time is important these days and versatile equipment is important. As stressed in the previous paragraph, edging can be accomplished with a trimmer in less time. On the rare occasions you may need one, the cost is impractical.
On initial clean ups is the only time I can see that you need one. If the grass and dirt is very thick or heavy coming over the edges all you will do is burn up the belt on the edger anyway or do other damage to it.
Bite the bullet and be a pro that knows what you are doing get the shovel and wheelbarrow rough that job in. Less time and no break downs. If it is that heavy of growth over the edge you will still have to shovel it up and haul it off. Then finish it with a trimmer or edger.
Relatively new to the industry, these stick edgers are the rave of commercial cutters and homeowners alike. Most brands now have both commercial and homeowner units. The stick edgers are light weight, easy to use and require less maintenance. I have also found them to be less expensive than traditional edgers.
These edgers take less time to do the job than rolling edgers and give the same results. They also can be used to create free form flower beds. You may not be able to have this item at first but eventually will find that having one will save you time. I've been told they are at least twice as fast as the push rolling edger.