Arabic Verb Conjugators

When learning Arabic, verbs are considered the most difficult. There are two sites that allow one to create conjugation of Arabic verbs from the root letters:

The first site is: http://qutrub.arabeyes.org/index#options The free downloadable qutrub software is beta version. I have found some verbs that are in the Quran and textbooks of classical Arabic, but qutrub sometimes gives the message:

Strangely, sometimes it continues to provide the conjugation for the allegedly gheir-saleh verb, and sometimes it does not. However, in overwhelming cases, the qutrub software, is good.

This site does not require one to have a knowledge of the type of verb. One can type the root letters with or without the vowels. In the latter case, if there are are more possibilities of vowels, the program gives a drop down list of the allowed combinations.

If one enters an invalid combination of letters or vowels, the program informs that the verb being sought is incorrect. Sometimes this looks like a false alarm, which may be due to an incorrect copy-paste. A new typing from the keyboard of the verb removes the false alarm. The root letters are not limited to three, and one can enter 4-letter and 5-letter roots as well. One drawback is that the interface is entirely in Arabic. One can also download a beta version of qutrub 0.5 which is a stand-alone small program, making it possible to work off-line. I prefer the off-line version. Here is part of website page:

and now look at part of a tasreef view from the stand-alone qutrub program:

The second site is: http://acon.baykal.be/ 
Most (but not all) Arab words, have a triliteral root, i.e. they come from combinations of three letters in the Arabic alphabet. One can select letters for each of the three parts of the root. This is a useful site, but somehow I am unable to understand how a person would know what the other two selections are for the verb: 1:- group (I-X) that the verb is supposed to belong to, and 2:- the vowels on (a, i, u) on each of the three letters of the root.

I just read on a blog (http://arabic-learners.blogspot.com/) that "don't trust it for weak-lettered verbs"