Is MATLAB OOP slow or am I doing something wrong?

I'm experimenting with MATLAB OOP, as a start I mimicked my C++'s Logger classes and I'm putting all my string helper functions in a String class, thinking it would be great to be able to do things like a + b, a == b, a.find( b ) instead of strcat( a b ), strcmp( a, b ), retrieve first element of strfind( a, b ), etc.

The problem: slowdown

I put the above things to use and immediately noticed a drastic slowdown. Am I doing it wrong (which is certainly possible as I have rather limited MATLAB experience), or does MATLAB's OOP just introduce a lot of overhead?

My test case

Here's the simple test I did for string, basically just appending a string and removing the appended part again:

Note: Don't actually write a String class like this in real code! Matlab has a native string array type now, and you should use that instead.

classdef String < handle
  ....
  properties
    stringobj = '';
  end
  function o = plus( o, b )
    o.stringobj = [ o.stringobj b ];
  end
  function n = Length( o )
    n = length( o.stringobj );
  end
  function o = SetLength( o, n )
    o.stringobj = o.stringobj( 1 : n );
  end
end

function atest( a, b ) %plain functions
  n = length( a );
  a = [ a b ];
  a = a( 1 : n );

function btest( a, b ) %OOP
  n = a.Length();
  a = a + b;
  a.SetLength( n );

function RunProfilerLoop( nLoop, fun, varargin )
  profile on;
  for i = 1 : nLoop
    fun( varargin{ : } );
  end
  profile off;
  profile report;

a = 'test';
aString = String( 'test' );
RunProfilerLoop( 1000, @(x,y)atest(x,y), a, 'appendme' );
RunProfilerLoop( 1000, @(x,y)btest(x,y), aString, 'appendme' );