Indeed he is but I do not see Turretin teaching the Free Offer in these extracts.Here is Turretin on the Offer as well as the will of God, election and reprobation.
"He, who by calling men shows that he wills their salvation and yet does not will it, acts deceitfully, if it is understood of the same will (i.e., if he shows that he wills that by the will of decree and yet does not will it; or by the will of precept and yet does not will it). But if it refers to diverse wills, the reasoning does not equally hold good. For example, if he shows that he wills a thing by the will of precept and yet does not will it by the will of decree, there is no simulation or hypocrisy here (as in prescribing the law to men, he shows that he wills they should fulfill it as to approbation and command, but not immediately as to decree). Now in calling God indeed shows that he wills the salvation of the called by the will of precept and good pleasure (euarestias), but not by the will of decree. For calling shows what God wills man should do, but not what he himself had decreed to do. It teaches what is pleasing and acceptable to God and in accordance with his own nature (namely, that the called should come to him); but not what he himself has determined to do concerning man. It signifies what God is prepared to give believers and penitents, but not what he has actually decreed to give to this or that person.
XVI. It is one thing to will reprobates to come (i.e., to command them to come and to desire it); another to will they should not come (i.e., to nill the giving them the power to come). God can in calling them will the former and yet not the latter without any contrariety because the former respects only the will of precept, while the latter respects the will of decree. Although these are diverse (because they propose diverse objects to themselves, the former the commanding of duty, but the latter the execution of the thing itself), still they are not opposite and contrary, but are in the highest degree consistent with each other in various respects. He does not seriously call who does not will the called to come (i.e., who does not command nor is pleased with his coming). But not he who does not will him to come whither he calls (i.e., did not intend and decree to come). For a serious call does not require that there should be an intention and purpose of drawing him, but only that there should be a constant will of commanding duty and bestowing the blessing upon him who performs it (which God most seriously wills). But if he seriously makes known what he enjoins upon the man and what is the way of salvation and what is agreeable to himself, God does not forthwith make known what he himself intended and decreed to do. Nor, if among men, a prince or a legislator commands nothing which he does not will (i.e., does not intend should also be done by his subjects because he has not the power of effecting this in them), does it follow that such is the case with God, upon whom alone it depends not only to command but also to effect this in man. But if such a legislator could be granted among men, he would rightly be said to will that which he approves and commands, although he does not intend to effect it.
XXI. The invitation to the wedding proposed in the parable (Mt. 22:1-14) teaches that the king wills (i.e., commands and desires) the invited to come and that this is their duty; but not that the king intends or has decreed that they should really come. Otherwise he would have given them the ability to come and would have turned their hearts. Since he did not do this, it is the surest sign that he did not will they should come in this way. When it is said “all things are ready” (Luke 14:17), it is not straightway intimated an intention of God to give salvation to them, but only the sufficiency of Christ’s sacrifice. For he was prepared by God and offered on the cross as a victim of infinite merit to expiate the sins of men and to acquire salvation for all clothed in the wedding garment and flying to him (i.e., to the truly believing and repenting) that no place for doubting about the truth and perfection of his satisfaction might remain.”
Turretin is smack on!